resolve: `resolver.with_module_lexical_scope()` needs testing

[jseyfried]

cc @nrc

[jseyfried]

cc @JohnHeitmann (c.f. #34655)

[Mark-Simulacrum]

@jseyfried This function is unused within this repository; can you comment on what kind of testing you mean? Is this compile-fail/run-pass tests? I don't think so; since it's unused.

[jseyfried]

@Mark-Simulacrum Unit testing that it behaves correctly.

[JohnTitor]

Triage: I'm going to close as outdated, since I cannot find this method in rustc_resolve now. If the method still exists somewhere and I overlook it, feel free to re-open.