fix(get_disu_kwargs): incorrect indexing of delr and delc

[langevin-usgs]

• delr is of size (ncol) and delc is of size (nrow). get_disu_kwargs had it wrong in a couple spots.
• Added test to show that the problem is fixed
• Updated get_disu_kwargs to optionally return vertices and cell2d

[codecov]

Codecov Report

Merging #2011 (47b080f) into develop (7cc5e6f) will increase coverage by 0.0%.
The diff coverage is 100.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #2011   +/-   ##
=======================================
  Coverage     72.7%   72.8%           
=======================================
  Files          259     259           
  Lines        58956   58992   +36     
=======================================
+ Hits         42916   42952   +36     
  Misses       16040   16040           

Files	Coverage Δ
flopy/utils/gridutil.py	98.1% <100.0%> (+0.3%)	⬆️