fix(map.py): fix slow plotting routines

[jlarsen-usgs]

*changed plotting routines to use QuadMesh and PathCollection
*fixed get_coords() issue with integer arrays

#1117 #1113

[codecov]

Codecov Report

Merging #1118 (0ba96e9) into develop (fbba027) will increase coverage by 0.683%.
The diff coverage is 87.755%.

❗ Current head 0ba96e9 differs from pull request most recent head de2e6c7. Consider uploading reports for the commit de2e6c7 to get more accurate results

@@              Coverage Diff              @@
##           develop     #1118       +/-   ##
=============================================
+ Coverage   71.729%   72.412%   +0.683%     
=============================================
  Files          225       221        -4     
  Lines        51919     51160      -759     
=============================================
- Hits         37241     37046      -195     
+ Misses       14678     14114      -564     

Impacted Files	Coverage Δ
flopy/discretization/grid.py	73.575% <50.000%> (-0.415%)	⬇️
flopy/discretization/structuredgrid.py	87.399% <84.615%> (+3.361%)	⬆️
flopy/discretization/vertexgrid.py	77.542% <84.615%> (+4.448%)	⬆️
flopy/plot/map.py	70.748% <94.736%> (ø)
flopy/discretization/unstructuredgrid.py	71.000% <100.000%> (+5.666%)	⬆️
flopy/mt3d/mtsft.py	6.569% <0.000%> (-72.263%)	⬇️
flopy/modflow/mfswi2.py	62.461% <0.000%> (-9.847%)	⬇️
flopy/modflow/mfoc.py	91.732% <0.000%> (-2.953%)	⬇️
flopy/utils/formattedfile.py	88.461% <0.000%> (-2.565%)	⬇️
flopy/modflow/mfbcf.py	87.939% <0.000%> (-2.011%)	⬇️
... and 10 more

[jlarsen-usgs]

@langevin-usgs

I can't recreate the unit test errors on my local machine. These errors seem to have something to do with head comparisons of MF6 output, which are sections of the code that are outside of the scope of these changes.

@spaulins-usgs
Any insight into what could be causing these failures?