Added maxsplit value in QualifiedName retrieval

[josieesh]

Summary

When working on another branch, noticed:

import a

foo = a.bar

The qualified name of a.bar would get returned as QualifiedName(name="a.b",...)

Test Plan

• All tests still passtox
• Check QualifiedName for a.bar is returned as "a.bar"

[codecov-commenter]

Codecov Report

Merging #312 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #312   +/-   ##
=======================================
  Coverage   93.96%   93.96%           
=======================================
  Files         223      223           
  Lines       21434    21441    +7     
=======================================
+ Hits        20141    20148    +7     
  Misses       1293     1293           

Impacted Files	Coverage Δ
libcst/metadata/scope_provider.py	97.11% <100.00%> (ø)
...cst/metadata/tests/test_qualified_name_provider.py	100.00% <100.00%> (ø)

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[jimmylai]

Nice finding.
Can you add a test cast?