Rollup merge of #137262 - compiler-errors:ast-ir-begone, r=lcnr

Make fewer crates depend on `rustc_ast_ir`

I think it simplifies the crate graph and also exposes people less to confusion if downstream crates don't interact with `rustc_ast_ir` directly and instead just use its functionality reexported through more familiar paths.

r? oli-obk since you introduced ast-ir

Author: matthiaskrgr