Revert "Revert "[clang][UBSan] Add implicit conversion check for bitfields"" (#87529)

Reverts llvm/llvm-project#87518

Revert is not needed as the regression was fixed with
1189e87951e59a81ee097eae847c06008276fef1.

I assumed the crash and warning are different issues, but according to
https://lab.llvm.org/buildbot/#/builders/240/builds/26629
fixing warning resolves the crash.

GitOrigin-RevId: 8a5a1b770413bb62ff27cd8c2aea3d04b3a95bbe
2 files changed