Summary

This PR enhances the C# ADBC driver's GetColumns functionality by adding a new BASE_TYPE_NAME column to the result set. This column provides the base type name without parameters or decorations, making it easier for clients to identify the fundamental data type regardless of its parameterization.

Proposed Changes

• Added a new BASE_TYPE_NAME column to the GetColumns result schema
• Enhanced the HiveServer2Statement class to process and populate the BASE_TYPE_NAME column
• Changed visibility modifiers for several methods from protected to public or internal to enable the enhancement
• Added support for the VARIANT SQL type in the SqlTypeNameParser
• Created comprehensive unit tests to verify the functionality with various data types

Implementation Details

The implementation:

1. Intercepts GetColumns query results
2. Processes each row to extract the base type name using the existing SetPrecisionScaleAndTypeName method
3. Adds the base type name as a new column in the result set
4. Preserves and potentially enhances precision and scale information for parameterized types

Benefits

• Simplifies client code that needs to identify base types (e.g., all DECIMAL types regardless of precision/scale)
• Maintains compatibility with existing code as this is an additive change
• Improves developer experience by providing clearer type information

Testing

Added comprehensive unit tests that verify:

• The presence of the BASE_TYPE_NAME column in GetColumns results
• Correct base type extraction for simple types
• Correct base type extraction for complex types (DECIMAL, INTERVAL, MAP, ARRAY, STRUCT)
• Precision and scale preservation for DECIMAL types
• Proper handling of type aliases (INT vs INTEGER)