update(_plot_package_helper): pass kwargs to datatype helpers

[jlarsen-usgs]

• change model_grid kwarg to modelgrid in _plot_model_helper

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d0c5dbc) 73.0% compared to head (68eab41) 71.3%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #2081     +/-   ##
=========================================
- Coverage     73.0%   71.3%   -1.7%     
=========================================
  Files          259     259             
  Lines        59329   59329             
=========================================
- Hits         43316   42334    -982     
- Misses       16013   16995    +982     

Files	Coverage Δ
flopy/plot/plotutil.py	55.2% <ø> (ø)

... and 59 files with indirect coverage changes