iceberg TableDefinition from table identifier

[devinrsmith]

It should be possible to get a TableDefinition (and potentially a meta_table representation) from a given table identifier without needing to read the table first.

[devinrsmith]

It probably needs to take into account IcebergInstructions; and have the same sort of logic that read_table would use to resolve the returned definition. If IcebergInstructions has a table definition that is incompatible, I would expect both get_definition and read_table to give similar error messages.

[rcaudy]

I think it makes sense to offer getDefinition(TableIdentifier) and getDefinition(TableIdentifier, Snapshot).

[rcaudy]

Prior art in core+, which we should match in spirit:

    @Override
    public TableDefinition getTableDefinition(@NotNull final String namespace, @NotNull final String tableName) {
        // return a definition derived from the Iceberg schema
    }

    @Override
    public Table getTableDefinitionTable(@NotNull final String namespace, @NotNull final String tableName) {
        return TableTools.newTable(getTableDefinition(namespace, tableName)).meta();
    }

[rcaudy]

Index: engine/table/src/main/java/io/deephaven/engine/util/TableTools.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/engine/table/src/main/java/io/deephaven/engine/util/TableTools.java b/engine/table/src/main/java/io/deephaven/engine/util/TableTools.java
--- a/engine/table/src/main/java/io/deephaven/engine/util/TableTools.java	(revision b9e2c6e3ba9f43e2ec69abe9176433503c87d054)
+++ b/engine/table/src/main/java/io/deephaven/engine/util/TableTools.java	(date 1722293086196)
@@ -14,6 +14,7 @@
 import io.deephaven.engine.rowset.RowSetFactory;
 import io.deephaven.engine.table.*;
 import io.deephaven.engine.table.impl.perf.QueryPerformanceRecorder;
+import io.deephaven.engine.table.impl.sources.NullValueColumnSource;
 import io.deephaven.internal.log.LoggerFactory;
 import io.deephaven.time.DateTimeUtils;
 import io.deephaven.engine.table.impl.QueryTable;
@@ -730,7 +731,7 @@
     public static Table newTable(TableDefinition definition) {
         Map<String, ColumnSource<?>> columns = new LinkedHashMap<>();
         for (ColumnDefinition<?> columnDefinition : definition.getColumns()) {
-            columns.put(columnDefinition.getName(), ArrayBackedColumnSource.getMemoryColumnSource(0,
+            columns.put(columnDefinition.getName(), NullValueColumnSource.getInstance(
                     columnDefinition.getDataType(), columnDefinition.getComponentType()));
         }
         return new QueryTable(definition, RowSetFactory.empty().toTracking(), columns) {