[CLIENT-1915] Refactor setup.py build script

[juliannguyen4]

• Don't build Python client if C client fails to build
• Remove unused variables
• README.rst is already included by default in MANIFEST.in, so we don't need to specify it
• Windows: compile C client without examples
• Officially support editable installs
• Compile Windows x64 wheels without flags used for gcc/clang

TODO:

• Wait for perf tests to be finished before making changes to compiler / linker flags
• Update docs about editable installs

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.45%. Comparing base (34c2e3f) to head (3137c31).
⚠️ Report is 9 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #832      +/-   ##
==========================================
+ Coverage   82.35%   82.45%   +0.09%     
==========================================
  Files          99       99              
  Lines       14379    14496     +117     
==========================================
+ Hits        11842    11952     +110     
- Misses       2537     2544       +7     

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