Consider access information when computing qualified names for nodes

[lpetre]

Summary

Scope.get_qualified_names_for has to do a lot of work to determine the qualified name for a node. The current version does not consider the data we have for accesses. If the given node is known to be an access, we can take advantage of that to work out the proper name.

This also means we now get the qualified names for string annotations for imports.

Test Plan

I've added a new test case in the QualifiedNameProviderTest to show the before/after effects of this change

[codecov-commenter]

Codecov Report

Merging #682 (8bf7c0f) into main (6e0c63a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #682   +/-   ##
=======================================
  Coverage   94.81%   94.81%           
=======================================
  Files         246      246           
  Lines       25607    25620   +13     
=======================================
+ Hits        24279    24292   +13     
  Misses       1328     1328           

Impacted Files	Coverage Δ
libcst/metadata/scope_provider.py	95.49% <100.00%> (+0.02%)	⬆️
libcst/metadata/tests/test_name_provider.py	100.00% <100.00%> (ø)

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[zsol]

lgtm!