fix(plot_pathline): update modpath intersection routines

[jlarsen-usgs]

• fix for mulitlayer grids
• added test_pathline_plot_xc to t049_test.py

#1108

[codecov]

Codecov Report

Merging #1112 (c15837a) into develop (fbba027) will increase coverage by 0.438%.
The diff coverage is 100.000%.

❗ Current head c15837a differs from pull request most recent head 536d476. Consider uploading reports for the commit 536d476 to get more accurate results

@@              Coverage Diff              @@
##           develop     #1112       +/-   ##
=============================================
+ Coverage   71.729%   72.167%   +0.438%     
=============================================
  Files          225       221        -4     
  Lines        51919     50480     -1439     
=============================================
- Hits         37241     36430      -811     
+ Misses       14678     14050      -628     

Impacted Files	Coverage Δ
flopy/plot/crosssection.py	60.169% <ø> (+4.457%)	⬆️
flopy/plot/plotutil.py	43.431% <100.000%> (+4.607%)	⬆️
flopy/mt3d/mtsft.py	5.535% <0.000%> (-73.298%)	⬇️
flopy/modflow/mfswi2.py	62.229% <0.000%> (-10.079%)	⬇️
flopy/export/metadata.py	15.833% <0.000%> (-6.475%)	⬇️
flopy/datbase.py	72.093% <0.000%> (-4.378%)	⬇️
flopy/discretization/modeltime.py	85.000% <0.000%> (-3.889%)	⬇️
flopy/modflow/mfswr1.py	20.930% <0.000%> (-3.515%)	⬇️
flopy/modflow/mfpbc.py	14.893% <0.000%> (-3.474%)	⬇️
flopy/modflow/mfsor.py	16.981% <0.000%> (-3.019%)	⬇️
... and 114 more