[clang] [Clang] Fix offsetof sign-extending unsigned array indices >= 128 (PR #204139)

[Marlus Cadanus da Costa via cfe-commits]

marlus wrote:

Resolved the conflict by rebasing on top of main and moving the release note entry to ReleaseNotes.md. The PR should be ready to merge now.

https://github.com/llvm/llvm-project/pull/204139