[clang] ✨ [Sema, Lex, Parse] Preprocessor embed in C and C++ (and Obj-C and Obj-C++ by-proxy) (PR #68620)

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h-vetinari wrote:

JeanHeyd wrote up a [blog post](https://thephd.dev/implementing-embed-c-and-c++) about this implementation, which is probably helpful as background material for any prospective reviewers. :)

https://github.com/llvm/llvm-project/pull/68620