Add constrained triangulation example

[akaszynski]

The docstring of the delaunay_2d filter is missing a constrained tesselation example.

import pyvista as pv

squar = pv.Polygon(n_sides=4, radius=8, fill=False).rotate_z(45, inplace=False)
circ0 = pv.Polygon(center=(2, 3, 0), n_sides=30, radius=1)
circ1 = pv.Polygon(center=(-2, -3, 0), n_sides=30, radius=1)
comb = circ0 + circ1 + squar
tess = comb.delaunay_2d(edge_source=comb)
tess.plot(cpos='xy')

---

As a bonus, converts optional to default in the docstring of this method.

[codecov]

Codecov Report

Merging #3448 (752318e) into main (8683da1) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3448      +/-   ##
==========================================
- Coverage   95.16%   95.16%   -0.01%     
==========================================
  Files          83       83              
  Lines       18476    18474       -2     
==========================================
- Hits        17583    17581       -2     
  Misses        893      893              

[banesullivan]

Would be great to plot comb before the triangulation to give more context

Otherwise, nice addition!

[akaszynski]

Suddenly seeing instability with:

reading sources... [ 19%] api/plotting/charts/_autosummary/pyvista.plotting.charts.Axis
Fatal Python error: Segmentation fault

Current thread 0x00007f837d79b740 (most recent call first):
  File "/home/runner/work/pyvista/pyvista/pyvista/plotting/plotting.py", line 4328 in _run_image_filter
  File "/home/runner/work/pyvista/pyvista/pyvista/plotting/plotting.py", line 4389 in get_image_depth
  File "/home/runner/work/pyvista/pyvista/pyvista/plotting/plotting.py", line 6093 in show
  File "/home/runner/work/pyvista/pyvista/pyvista/plotting/charts.py", line 1438 in show
  File "/home/runner/work/pyvista/pyvista/pyvista/plotting/charts.py", line 113 in mem_sub
  File "<string>", line 4 in <module>
  File "/home/runner/work/pyvista/pyvista/pyvista/ext/plot_directive.py", line 328 in _run_code
  File "/home/runner/work/pyvista/pyvista/pyvista/ext/plot_directive.py", line 367 in render_figures
  File "/home/runner/work/pyvista/pyvista/pyvista/ext/plot_directive.py", line 502 in run
  File "/home/runner/work/pyvista/pyvista/pyvista/ext/plot_directive.py", line 173 in run

Looks like a charts issue, but it's unclear what's causing it.

[tkoyama010]

Thanks for adding this. I am excited about this example.

[akaszynski]

Going ahead and merging this. Would like to get the release process out soon and changes have been implemented. Thanks @banesullivan and @tkoyama010 for your reviews!