[clang] [clang-tools-extra] [llvm] [clang] Introduce diagnostics suppression mappings (PR #112517)

[Boaz Brickner via llvm-commits]

https://github.com/bricknerb requested changes to this pull request.

Note that there are a few open comments from previous iterations.

https://github.com/llvm/llvm-project/pull/112517