[clang] [CIR] Build out AST consumer patterns to reach the entry point into CIRGen (PR #91007)

[Bruno Cardoso Lopes via cfe-commits]

https://github.com/bcardosolopes approved this pull request.

Seems like all issues have been addressed? Anything remaining @AaronBallman ?

Thanks everyone for all the reviews!

https://github.com/llvm/llvm-project/pull/91007