save-analysis: emit names of items that a glob import actually imports.

There is also some work here to make resolve a bit more stable - it no longer overwrites a specific import with a glob import.

[breaking-change]

Name resolution previously had a bug where you could import an item multiple times using globs without the unused import lint noticing. That is fixed, so if you have the unused import lint on, then you may get alerted to unused imports.
Add some impls of Show (RefCell, Weak, some resolve types)
Fix fallout
auto merge of #19254 : nick29581/rust/dxr-glob, r=pcwalton

There is also some work here to make resolve a bit more stable - it no longer overwrites a specific import with a glob import.

r?