fix(bqjdbc): resolve JDBC metadata compliance gaps for wrappers, searchability, and type mappings

[Neenu1995]

b/514445832

Key Changes

1. Align DatabaseMetaData Column Data Types and DB-Specific Type Names:

• Updated DatabaseMetaData.getColumns() type resolution (via mapBigQueryTypeToJdbc) to map BigQuery types and database-specific type names compliantly (e.g., STRING, RANGE, GEOGRAPHY, JSON, INTERVAL).
• Aligned type codes with JDBC conventions (e.g., StandardSQLTypeName.STRING maps to Types.NVARCHAR to support Unicode/UTF-8 string reporting).
• Ensured that unknown/fallback types default to Types.NVARCHAR / STRING instead of Types.VARCHAR to keep mapping behavior consistent across the driver.
• Documented design rationale for mapping StandardSQLTypeName.STRING to Types.NVARCHAR (UTF-8 character encoding reporting).

2. Wrapper Pattern Implementation (JDBC 4.0 Compliance):

• Implemented standard JDBC wrapper methods (unwrap and isWrapperFor) in BigQueryDatabaseMetaData and BigQueryResultSetMetadata.
• Integrated proxy resolution via BigQueryJdbcContextProxy to correctly handle unwrapping in connection proxy environments.

3. ResultSetMetaData Searchability:

• Refactored BigQueryResultSetMetadata.isSearchable to return true for all column types. This fixes compliance issues where advanced types (GEOGRAPHY, JSON, INTERVAL, RANGE under Types.OTHER) were incorrectly reported as not searchable, even though they are fully queryable.

[gemini-code-assist]

Code Review

This pull request refactors the type mapping logic in BigQueryDatabaseMetaData by introducing a static STANDARD_TYPE_INFO map and updates several BigQuery-to-JDBC type mappings, such as changing the default string representation to NVARCHAR and mapping complex types like GEOGRAPHY and JSON to Types.OTHER. Additionally, it implements the unwrap and isWrapperFor methods in BigQueryDatabaseMetaData, BigQueryResultSetMetadata, and the JDBC context proxy to support standard JDBC wrapper operations. Corresponding unit tests have been updated and expanded to verify these changes. I have no feedback to provide as there were no review comments to assess.