fix(grid): add vertices_coords init parameter

[wpbonelli]

Add a parameter vertices_coords to VertexGrid and UnstructuredGrid init methods, indicating whether vertices are in local or global coordinates. Default to "local". This fixes #2388 by making it possible to avoid repeating the coordinate transformation. The parameter is not applicable to StructuredGrid because vertex coordinates are not provided to its init method.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.3%. Comparing base (556c088) to head (0aedfd4).
⚠️ Report is 119 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2687      +/-   ##
===========================================
+ Coverage     55.5%    72.3%   +16.8%     
===========================================
  Files          644      667      +23     
  Lines       124135   130304    +6169     
===========================================
+ Hits         68947    94295   +25348     
+ Misses       55188    36009   -19179     

Files with missing lines	Coverage Δ
flopy/discretization/unstructuredgrid.py	81.2% <100.0%> (-0.3%)	⬇️
flopy/discretization/vertexgrid.py	80.3% <100.0%> (-3.3%)	⬇️

... and 561 files with indirect coverage changes

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[wpbonelli]

After a closer look I see that the same double transform issue applies to cell centers too for unstructured grids. But not vertex grids, which calculate cell centers from vertices. So a new parameter should apply not only to vertices but to any manually specified grid feature coordinates. So it should probably be named differently. Maybe global_xy? This is consistent with a similar parameter in mp7particledata.py, the only difference is that one controls what is output and this one will indicate what is provided as input.

[wpbonelli]

decided against this approach after discussion with @jlarsen-usgs @jdhughes-dev