Port pyre fixes

[stroxler]

Summary

Because it isn't feasible to continuously push new releases of LibCST, we vendored a copy of
_apply_type_annotations.py into the pyre codebase so that we could rapidly improve pyre infer.

But as a result several bugfixes have wound up in pyre that belong here. This commit closes the
gap.

Each commit is either:

• a test harness commit, setting up (undesirable) test results that we'll fix in the next, or
• a port from a change made to pyre, whose commit message points to the original commit

Test Plan

> python -m unittest libcst.codemod.visitors.tests.test_apply_type_annotations
.....................................................................
----------------------------------------------------------------------
Ran 69 tests in 7.039s

OK

[codecov-commenter]

Codecov Report

Merging #651 (e32ec57) into main (f2cd39c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #651   +/-   ##
=======================================
  Coverage   94.78%   94.78%           
=======================================
  Files         247      247           
  Lines       25376    25378    +2     
=======================================
+ Hits        24052    24054    +2     
  Misses       1324     1324           

Impacted Files	Coverage Δ
...emod/visitors/tests/test_apply_type_annotations.py	100.00% <ø> (ø)
libcst/codemod/visitors/_apply_type_annotations.py	95.45% <100.00%> (+<0.01%)	⬆️
libcst/metadata/tests/test_scope_provider.py	99.88% <0.00%> (+<0.01%)	⬆️

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