[clang] [Clang][TableGen] Add documentation generation infrastructure for builtins (PR #181573)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Oh I see. I did check the code in `clang/utils/TableGen/ClangAttrEmitter.cpp`. There is not too much value of doing that since the shared code is really not that much.

Figured it could be a shared header if there's common handling of the documentation string but they are likely using slightly different formats.

https://github.com/llvm/llvm-project/pull/181573