Add operator to ESQL signature for kibana

This adds a field to the kibana defintion files for each signature that
looks like:
```
  "operator": "+",
```
Kibana wants these symbols.

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/FunctionInfo.java

@@ -18,6 +18,15 @@
 @Retention(RetentionPolicy.RUNTIME)
 @Target(ElementType.CONSTRUCTOR)
 public @interface FunctionInfo {
+    /**
+     * If this function implements an operator, what is its symbol?
+     * <p>
+     *     This exists entirely to add to the Kibana function definition
+     *     json files.
+     * </p>
+     */
+    String operator() default "";
+
     /**
      * The type(s) this function returns.
      */

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/fulltext/Match.java

@@ -98,6 +98,7 @@ public class Match extends FullTextFunction implements PostOptimizationVerificat
 
     @FunctionInfo(
         returnType = "boolean",
+        operator = "MATCH",
         preview = true,
         description = """
             Use `MATCH` to perform a <<query-dsl-match-query,match query>> on the specified field.

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RLike.java

@@ -30,7 +30,7 @@
 public class RLike extends org.elasticsearch.xpack.esql.core.expression.predicate.regex.RLike implements EvaluatorMapper {
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "RLike", RLike::new);
 
-    @FunctionInfo(returnType = "boolean", description = """
+    @FunctionInfo(returnType = "boolean", operator = "RLIKE", description = """
         Use `RLIKE` to filter data based on string patterns using using
         <<regexp-syntax,regular expressions>>. `RLIKE` usually acts on a field placed on
         the left-hand side of the operator, but it can also act on a constant (literal)

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/WildcardLike.java

@@ -35,7 +35,7 @@ public class WildcardLike extends org.elasticsearch.xpack.esql.core.expression.p
         WildcardLike::new
     );
 
-    @FunctionInfo(returnType = "boolean", description = """
+    @FunctionInfo(returnType = "boolean", operator = "LIKE", description = """
         Use `LIKE` to filter data based on string patterns using wildcards. `LIKE`
         usually acts on a field placed on the left-hand side of the operator, but it can
         also act on a constant (literal) expression. The right-hand side of the operator

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/arithmetic/Add.java

@@ -36,6 +36,7 @@ public class Add extends DateTimeArithmeticOperation implements BinaryComparison
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "Add", Add::new);
 
     @FunctionInfo(
+        operator = "+",
         returnType = { "double", "integer", "long", "date_nanos", "date_period", "datetime", "time_duration", "unsigned_long" },
         description = "Add two numbers together. " + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`."
     )

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/arithmetic/Div.java

@@ -29,6 +29,7 @@ public class Div extends EsqlArithmeticOperation implements BinaryComparisonInve
     private DataType type;
 
     @FunctionInfo(
+        operator = "/",
         returnType = { "double", "integer", "long", "unsigned_long" },
         description = "Divide one number by another. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/arithmetic/Mod.java

@@ -26,6 +26,7 @@ public class Mod extends EsqlArithmeticOperation {
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "Mod", Mod::new);
 
     @FunctionInfo(
+        operator = "%",
         returnType = { "double", "integer", "long", "unsigned_long" },
         description = "Divide one number by another and return the remainder. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`."

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/arithmetic/Mul.java

@@ -26,6 +26,7 @@ public class Mul extends EsqlArithmeticOperation implements BinaryComparisonInve
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "Mul", Mul::new);
 
     @FunctionInfo(
+        operator = "*",
         returnType = { "double", "integer", "long", "unsigned_long" },
         description = "Multiply two numbers together. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`."

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/arithmetic/Neg.java

@@ -37,6 +37,7 @@ public class Neg extends UnaryScalarFunction {
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "Neg", Neg::new);
 
     @FunctionInfo(
+        operator = "-",
         returnType = { "double", "integer", "long", "date_period", "time_duration" },
         description = "Returns the negation of the argument."
     )

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/arithmetic/Sub.java

@@ -38,6 +38,7 @@ public class Sub extends DateTimeArithmeticOperation implements BinaryComparison
     public static final NamedWriteableRegistry.Entry ENTRY = new NamedWriteableRegistry.Entry(Expression.class, "Sub", Sub::new);
 
     @FunctionInfo(
+        operator = "-",
         returnType = { "double", "integer", "long", "date_period", "datetime", "time_duration", "unsigned_long" },
         description = "Subtract one number from another. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`."

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/Equals.java

@@ -49,6 +49,7 @@ public class Equals extends EsqlBinaryComparison implements Negatable<EsqlBinary
     );
 
     @FunctionInfo(
+        operator = "==",
         returnType = { "boolean" },
         description = "Check if two fields are equal. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/GreaterThan.java

@@ -44,6 +44,7 @@ public class GreaterThan extends EsqlBinaryComparison implements Negatable<EsqlB
     );
 
     @FunctionInfo(
+        operator = ">",
         returnType = { "boolean" },
         description = "Check if one field is greater than another. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/GreaterThanOrEqual.java

@@ -44,6 +44,7 @@ public class GreaterThanOrEqual extends EsqlBinaryComparison implements Negatabl
     );
 
     @FunctionInfo(
+        operator = ">=",
         returnType = { "boolean" },
         description = "Check if one field is greater than or equal to another. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/In.java

@@ -108,6 +108,7 @@ public class In extends EsqlScalarFunction {
     private final List<Expression> list;
 
     @FunctionInfo(
+        operator = "IN",
         returnType = "boolean",
         description = "The `IN` operator allows testing whether a field or expression equals an element in a list of literals, "
             + "fields or expressions.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/LessThan.java

@@ -44,6 +44,7 @@ public class LessThan extends EsqlBinaryComparison implements Negatable<EsqlBina
     );
 
     @FunctionInfo(
+        operator = "<",
         returnType = { "boolean" },
         description = "Check if one field is less than another. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/LessThanOrEqual.java

@@ -44,6 +44,7 @@ public class LessThanOrEqual extends EsqlBinaryComparison implements Negatable<E
     );
 
     @FunctionInfo(
+        operator = "<=",
         returnType = { "boolean" },
         description = "Check if one field is less than or equal to another. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/predicate/operator/comparison/NotEquals.java

@@ -49,6 +49,7 @@ public class NotEquals extends EsqlBinaryComparison implements Negatable<EsqlBin
     );
 
     @FunctionInfo(
+        operator = "!=",
         returnType = { "boolean" },
         description = "Check if two fields are unequal. "
             + "If either field is <<esql-multivalued-fields,multivalued>> then the result is `null`.",

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/AbstractFunctionTestCase.java

@@ -1146,7 +1146,13 @@ private static void renderKibanaFunctionDefinition(
             "comment",
             "This is generated by ESQL's AbstractFunctionTestCase. Do no edit it. See ../README.md for how to regenerate it."
         );
-        builder.field("type", isAggregation() ? "agg" : OPERATORS.get(name) != null ? "operator" : "eval");
+        if (false == info.operator().isEmpty()) {
+            builder.field("type", "operator");
+            builder.field("operator", info.operator());
+            assertThat(isAggregation(), equalTo(false));
+        } else {
+            builder.field("type", isAggregation() ? "agg" : "eval");
+        }
         builder.field("name", name);
         builder.field("description", removeAsciidocLinks(info.description()));
         if (Strings.isNullOrEmpty(info.note()) == false) {