- Enable renameColumn, alterExistingColumn, alterType, alterNullability,
alterDefault, comment, and indexComment capabilities for SQL Server
- Implement build_sqlserver_existing_column_sql() with sp_rename for column
rename, ALTER TABLE ALTER COLUMN for type/nullability changes, and dynamic
SQL for default constraint management
- Add sp_addextendedproperty/sp_dropextendedproperty DDL generation for table,
column, and index comments
- Fetch table and column comments from sys.extended_properties via OUTER APPLY
in list_tables, list_objects, and get_columns SQL queries
- Fix table comment placeholder text (was showing column comment placeholder)