`ADD` and `DROP SIGNATURE` Support

I checked the StoredProcedure and Certificate object and did not find any way to check for signature or ADD or DROP the signature. Is this feature supported?

I worked around the issue by using straight T-SQL including sys.fn_check_object_signatures and DROP SIGNATURE to clean up some certificate work.

首先检查 issue 中提到的 StoredProcedure 和 Certificate 对象，然后将它们的 API 与所引用的 T-SQL 操作 sys.fn_check_object_signatures、ADD SIGNATURE 和 DROP SIGNATURE 进行比较。当通过实现或记录在案的限制，明确确立 API 支持的签名检查和管理行为时，即视为完成。