[clang] [CIR] Make the post-CIRGen emission path independent of ASTContext (PR #229441)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

How does this accomplish the task?  It still has the same reference to AST Context, right?  And doesn't a lot of hte backend consumer stuff already exist in a shared location?  Should we use that instead?

https://github.com/llvm/llvm-project/pull/229441