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

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cor3ntin wrote:

@StephanTLavavej @CaseyCarter What is your timetable? I'm wondering whether we should do any back port effort (otherwise it will land in Clang 20 in ~february)

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