[clang] [clang] Deduce _BitInt(N) template parameter as size_t (PR #195534)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin commented:

I think the change make sense. I'd like Erich opinion though.

This change needs a release note.
Please add an entry to `clang/docs/ReleaseNotes.rst` in the section the most adapted to the change, and referencing any Github issue this change fixes. Thanks!

We might want to mention that in the potential breaking change section, it has the potential to be both an api and abi break (which i think is reasonable, it just needs to be mentioned) 

https://github.com/llvm/llvm-project/pull/195534