[SPARK-29941][SQL] Add ansi type aliases for char and decimal

### What changes were proposed in this pull request?

Checked with SQL Standard and PostgreSQL

> CHAR is equivalent to CHARACTER. DEC is equivalent to DECIMAL. INT is equivalent to INTEGER. VARCHAR is equivalent to CHARACTER VARYING. ...

```sql
postgres=# select dec '1.0';
numeric
---------
1.0
(1 row)

postgres=# select CHARACTER '. second';
  bpchar
----------
 . second
(1 row)

postgres=# select CHAR '. second';
  bpchar
----------
 . second
(1 row)
```

### Why are the changes needed?

For better ansi support
### Does this PR introduce any user-facing change?

yes, we add character as char and dec as decimal

### How was this patch tested?

add ut

Closes #26574 from yaooqinn/SPARK-29941.

Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala

@@ -2153,12 +2153,12 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
       case ("date", Nil) => DateType
       case ("timestamp", Nil) => TimestampType
       case ("string", Nil) => StringType
-      case ("char", length :: Nil) => CharType(length.getText.toInt)
+      case ("character" | "char", length :: Nil) => CharType(length.getText.toInt)
       case ("varchar", length :: Nil) => VarcharType(length.getText.toInt)
       case ("binary", Nil) => BinaryType
-      case ("decimal", Nil) => DecimalType.USER_DEFAULT
-      case ("decimal", precision :: Nil) => DecimalType(precision.getText.toInt, 0)
-      case ("decimal", precision :: scale :: Nil) =>
+      case ("decimal" | "dec", Nil) => DecimalType.USER_DEFAULT
+      case ("decimal" | "dec", precision :: Nil) => DecimalType(precision.getText.toInt, 0)
+      case ("decimal" | "dec", precision :: scale :: Nil) =>
         DecimalType(precision.getText.toInt, scale.getText.toInt)
       case ("interval", Nil) => CalendarIntervalType
       case (dt, params) =>

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/DataTypeParserSuite.scala

@@ -51,10 +51,13 @@ class DataTypeParserSuite extends SparkFunSuite {
   checkDataType("dOUBle", DoubleType)
   checkDataType("decimal(10, 5)", DecimalType(10, 5))
   checkDataType("decimal", DecimalType.USER_DEFAULT)
+  checkDataType("Dec(10, 5)", DecimalType(10, 5))
+  checkDataType("deC", DecimalType.USER_DEFAULT)
   checkDataType("DATE", DateType)
   checkDataType("timestamp", TimestampType)
   checkDataType("string", StringType)
   checkDataType("ChaR(5)", StringType)
+  checkDataType("ChaRacter(5)", StringType)
   checkDataType("varchAr(20)", StringType)
   checkDataType("cHaR(27)", StringType)
   checkDataType("BINARY", BinaryType)