resolve: Support imports of associated types and glob imports from traits

[petrochenkov]

Follow up to #134754, part of #134691.
This PR also closes #138711 now.

Prohibiting use Trait::AssocType; at name resolution stage doesn't make sense, the name itself is perfectly resolveable.
It's a type checker's problem that the necessary generic args are not passed when the imported AssocType is used, so an error should be reported there.

And since we can import associated trait items now, glob imports from traits can also be allowed.

[rustbot]

r? @wesleywiser

rustbot has assigned @wesleywiser.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rustbot]

HIR ty lowering was modified

cc @fmease

[fmease]

I'm fine with lifting the restrictions from the resolver and with making HIR ty lowering responsible for dealing with it, although this PR would allow more code to compile under the unstable feature (trait T { type A; } use T::A; would start compiling (notice the lack of any use sites of A!)) plus glob imports, of course.

This deviates from the RFC. IIRC it's fine for me as a T-compiler member to approve such a change regardless and without T-lang input as long as we clearly state all of this in the tracking issue #134691, so any hypothetical future stabilization report and T-lang stabilization FCP can pick up on it.

[petrochenkov]

@rustbot ready