fix(csharp/src/Drivers): Add FK_NAME and KEQ_SEQ fields to GetColumnsExtended and improve type handling

[eric-wang-1990]

Description

This PR enhances the C# implementation of GetColumnsExtended by:

1. Adding FK_NAME and KEQ_SEQ fields to the foreign key fields array
2. Improving type handling in the relationship data processing to properly handle non-string types like Int32
3. Preserving original field types from the source schema in the extended results
4. Removing unnecessary underscore escaping in GetCrossReferenceAsForeignTableAsync since these are exact match queries
5. Adding schema validation tests for the extended column metadata
6. Fix the empty foreign key result set name Key_seq to Keq_seq

Rationale

These changes ensure that all necessary foreign key relationship information is available to clients and that the data types are properly preserved when processing relationship data. The additional fields (FK_NAME and KEQ_SEQ) provide important context about foreign key constraints.

Testing

• Enhanced existing tests to validate the schema of the GetColumnsExtended result
• Verified proper type handling for both string and integer fields
• Manually tested with Hive and Databricks connections

[CurtHagenlocher]

Thanks!

[CurtHagenlocher]

This column name will never not make me crack up while simultaneously saddening me :/.