[clang] [clang-tools-extra] [clang][CodeComplete] skip explicit obj param in SignatureHelp (PR #146649)

[Mythreya Kuricheti via cfe-commits]

MythreyaK wrote:

> Hah, it's from the removal of the s at the end of a.$c1^s! I guess there was a reason for it 😆

You're right, nice catch! I thought the 's' was from me not `Ctrl+S` correctly 😆. 

> I'm ok with either option.

I'm not sure what the changes might be, so I my thought is that if we can get the tests in, we'll be able to monitor behavior changes. 

> It's fine to assert the current (buggy) behaviour, but please add a comment describing why it's wrong, and what we should get instead.

Added a few `TODO`s, do they look okay? 

https://github.com/llvm/llvm-project/pull/146649