[clang] [mlir] [CIR] Add tons of function infra, plus a handful of attributes (PR #179811)

[Tobias Gysi via cfe-commits]

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

LGTM from the LLVM dialect side modulo comments.

The default_func_attrs would be a good candidate for the passthrough - even when lowering from CIR - I think. However, given the call operation doesn't have a passthrough attribute the solution in the PR seems justified. 

https://github.com/llvm/llvm-project/pull/179811