[clang] Fix false negative when value initializing a field annotated with [[clang::require_field_initialization]] (PR #124329)

[via cfe-commits]

higher-performance wrote:

> this would need to be backported (https://releases.llvm.org/19.1.0/docs/GitHub.html#backporting-fixes-to-the-release-branches).

Oh, @AaronBallman - would you mind adding this as a milestone so I can `/cherry-pick` here?

https://github.com/llvm/llvm-project/pull/124329