Refactor silhouette from add_mesh

[MatthewFlamm]

Overview

add_mesh is a monster and the logic is very complex depending on combinations of input parameters. I think it is best if we can extract out as much logic as possible into separable pieces. Silhouette functionality is completely separate from all the other pieces. This PR separates out the silhouette functionality into it's own method, that can be called on it's own if desired. add_mesh calls this new method.

Details

My personal style preference would be to have the below for any functionality like this:

plotter.add_mesh(mesh)
plotter.add_silhouette(mesh)

This makes it more clear that we have two separate actors being added to the scene. I'm not sure if the current state has problems. If the mesh is updated, will the silhouette also update? In any case, separating out the logic is the first step.

TODO:

• Docstring
• Examples for docstring where new method is called directly
• Test where new method is called directly

[codecov]

Codecov Report

Merging #1689 (b380b44) into main (9d05d4d) will decrease coverage by 0.00%.
The diff coverage is 96.42%.

@@            Coverage Diff             @@
##             main    #1689      +/-   ##
==========================================
- Coverage   92.59%   92.59%   -0.01%     
==========================================
  Files          71       71              
  Lines       13864    13870       +6     
==========================================
+ Hits        12838    12843       +5     
- Misses       1026     1027       +1     

[akaszynski]

Still failing due to:

WARNING: [numpydoc] Validation warnings while processing docstring for 'pyvista.Plotter.add_silhouette':
PR07: Parameter "mesh" has no description
RT01: No Returns section found

+100 for cleaning up add_mesh. I've done a little bit in #1685

[akaszynski]

Nice work! I made some minor changes to get the links to build correctly, but otherwise LGTM.