Add support for `use Trait::func`

https://github.com/rust-lang/rfcs/pull/3591 is likely to be introduced to the language, which will require some changes to our early name resolution, notably this change ties in trait assoc items into early name resolution so our corresponding DefMap query will have to collect and expand macros in trait assoc item position, replacing the current trait_data query. This will unfortunately slow down def map creation and also invalidate it when trait assoc item signatures are changed but that's just the nature of moving things into early nameres. OTOH this does get rid of one of the more frequent queries which might slightly reduce memory usage/or improve perf in other ways.

Note this hasn't been accepted yet so there is little reason to implement that right now.