[clang] [Inliner] Improve attribute propagation to callsites when inlining. (PR #66036)

[Johannes Doerfert via cfe-commits]

jdoerfert wrote:

> > I don't think 10 commit PRs are helpful. This should be 3 PRs at least. One is trivial, one is probably easy, and then one with the new stuff.
> 
> So PR based on PR? The thing is there are dependencies between commits. My expectation is that I will push commits as they are approved, not the whole PR at once.

We always had dependences between commits. Just mention it in the commit message. 
This PR contains arguably different things. It simply makes it harder to review it. The guidance on this is clear, make review chunks as small if possible. The RFC commits, the fix, and the new functionality do not need to be commingled. 

https://github.com/llvm/llvm-project/pull/66036