[clang] [clang] Implement CWG2627 Bit-fields and narrowing conversions (PR #78112)

[Mital Ashok via cfe-commits]

MitalAshok wrote:

@AaronBallman This shouldn't affect C at all since this is only about non-constant-expressions which come from a bit-field

https://github.com/llvm/llvm-project/pull/78112