fix: realpath on windows changed behavior in python 3.8 to expand mapped drive letters to their UNC path names

[cfxegbert]

Fixes #1438

os.path.realpath on Python 3.8 Windows changed. When resolving mapped drive realpath returns the UNC path without the drive letter.

This pull restores the Python 3.7 Windows behavior of realpath being a wrapper around abspath. The behavior can be changed with the rezconfig setting windows_unc_path

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 59.31%. Comparing base (491497f) to head (0903ec3).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/rez/rezconfig.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1856      +/-   ##
==========================================
+ Coverage   59.30%   59.31%   +0.01%     
==========================================
  Files         126      126              
  Lines       17210    17217       +7     
  Branches     3015     3016       +1     
==========================================
+ Hits        10206    10212       +6     
- Misses       6319     6320       +1     
  Partials      685      685              

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