[clang] [clang] Simplify the overload resolution logic for operator new and new[] (PR #211482)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> Don't you think making this patch NFC and moving all diagnostic changes to separate patches would be better?

This PR has done its best to not change diagnostics in any way -- the diagnostics in the associated tests are either additional subtests of behavior that was previously untested or completely new tests specifically for the purpose of testing diagnostics and edge cases that were not previously covered.

https://github.com/llvm/llvm-project/pull/211482