fix(gridgen): support arbitrary path-like for shapefiles

[wpbonelli]

• close .shp always appended to filename, even if it already has .shp extension (gridgen module) #2024
• follow up to fix(gridgen): only add suffix for generated shpfiles #2022
• support arbitrary paths as feature/features params to add_active_domain()/add_refinement_feature()
• support and test shapefile names with/without ".shp" extension (for backwards-compatibility)
• use ValueError instead of Exception where appropriate

[codecov]

Codecov Report

Merging #2026 (39574f5) into develop (b3510e9) will increase coverage by 0.0%.
Report is 1 commits behind head on develop.
The diff coverage is 75.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2026   +/-   ##
=======================================
  Coverage     72.8%   72.8%           
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  Files          259     259           
  Lines        59042   59043    +1     
=======================================
+ Hits         43028   43029    +1     
  Misses       16014   16014           

Files	Coverage Δ
flopy/utils/gridgen.py	86.8% <75.0%> (+<0.1%)	⬆️