Replace `ScalarUDFImpl::{equals,hash_value}` with `UdfHash`, `UdfEq` traits

[findepi]

Implement proposal set forth in #16677 (comment)

• depends on Derive UDF (ScalarUDFImpl) equality from PartialEq, Hash #16865
• depends on Implement PartialEq, Hash for all UDFs (ScalarUDFImpl) #16868