fix(bqjdbc): metadata methods & getSqlTypeName for struct

[logachev]

b/502644660
b/502643873

• Fix various metadata bool methods
• Return 'STRUCT' as SqlType name for Struct methods, name chosen due to
  • Matches the keyword for anonymous structured types in modern BigQuery Standard SQL.
  • Consistent with how the generic structural type is identified in the Google Cloud BigQuery Java SDK (StandardSQLTypeName.STRUCT).

[gemini-code-assist]

Code Review

This pull request updates the BigQuery JDBC driver to enable support for catalog-related metadata operations and batch updates. Additionally, it implements the getSQLTypeName method in BigQueryBaseStruct to return 'STRUCT' and updates the relevant unit tests. Feedback was provided to replace the hardcoded 'STRUCT' string with the StandardSQLTypeName.STRUCT.name() constant to improve maintainability and consistency with the BigQuery SDK.