[clang] Add ParserConversionAction (PR #169803)

[Abhina Sree via cfe-commits]

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abhina-sree wrote:

In this paper https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2361r4.pdf it mentions `Allow numeric escape sequences in asm statements.` I think we cannot treat asm strings as an unevaluated string as a result

https://github.com/llvm/llvm-project/pull/169803