Rollup merge of #69965 - mark-i-m:codegen-utils, r=eddyb

Rollup merge of #69965 - mark-i-m:codegen-utils, r=eddyb

Refactorings to get rid of rustc_codegen_utils

r? @eddyb

cc #45276

After this, the only modules left in `rustc_codegen_utils` are
- `link`: a bunch of linking-related functions (many dealing with file names). These are mostly consumed by save analysis, rustc_driver, rustc_interface, and of course codegen. I assume they live here because we don't want a dependency of save analysis on codegen... Perhaps they can be moved to librustc?
- ~`symbol_names` and `symbol_names_test`: honestly it seems odd that `symbol_names_test` is not a submodule of `symbol_names`. It seems like these could honestly live in their own crate or move to librustc. Already name mangling is exported as the `symbol_name` query.~ (move it to its own crate)

I don't mind doing either of the above as part of this PR or a followup if you want.