[clang] [clang-cl]: Add /std:c++23preview and update _MSVC_LANG for C++23 (PR #112378)

[Stephan T. Lavavej via cfe-commits]

StephanTLavavej wrote:

We can use `-Xclang -std=c++23` as a workaround, so we don't need a backport.

https://github.com/llvm/llvm-project/pull/112378