[clang] [Clang] support C23 constexpr struct member access in constant expressions (PR #182770)

[Mariya Podchishchaeva via cfe-commits]

https://github.com/Fznamznon approved this pull request.

LGTM, @AaronBallman could you please take a look too?

https://github.com/llvm/llvm-project/pull/182770