[clang] [llvm] [clang] Add test run of 'dump_ast_matchers.py' (PR #165472)

[Aaron Ballman via llvm-commits]

https://github.com/AaronBallman commented:

Hmmm, instead of getting a precommit CI failure when forgetting to run the AST documentation generator, we should be running the documentation generator on-demand in the backend like we do for generating docs from attributes or diagnostics and then nobody has to remember to do that step ever.

This is still a step in the right direction, so I'm not opposed.

https://github.com/llvm/llvm-project/pull/165472