Make scale config apply to variables computed by the stat transform

[mwaskom]

• Refactors _transform_coords and _setup_scales into one method.
• Properly handles scale config for coordinate variables that are computed during the stat
• Properly handles scale config when only coordinate ranges are defined

Fixes #2908, fixes #2885

[codecov]

Codecov Report

Merging #2915 (1ab0e55) into master (1524d43) will increase coverage by 0.01%.
The diff coverage is 98.23%.

@@            Coverage Diff             @@
##           master    #2915      +/-   ##
==========================================
+ Coverage   98.20%   98.22%   +0.01%     
==========================================
  Files          69       69              
  Lines       22666    22694      +28     
==========================================
+ Hits        22260    22291      +31     
+ Misses        406      403       -3     

Impacted Files	Coverage Δ
seaborn/_core/plot.py	95.33% <97.40%> (+0.39%)	⬆️
seaborn/_compat.py	30.26% <100.00%> (+1.88%)	⬆️
tests/_core/test_plot.py	98.49% <100.00%> (+0.04%)	⬆️