[clang] [Clang] Fix FixIt for implicit-int diagnostics. (PR #179356)

[Karl Friebel via cfe-commits]

KFAFSP wrote:

The latest commit passes the whole test suite on my machine and addresses the comments made by Sirraide:

- Changed `implicit-int` diagnostics to only emit one per DeclGroup (in the most straight-forward way possible).
- Added additional release note detailing this new behavior.
- Fixed typo in old release note.
- Added a couple more tests for other combinations of specifiers.

https://github.com/llvm/llvm-project/pull/179356