Add 3D figure rendering to documentation

[hoechenberger]

we don't support pyvista and 3D plots in the doc of mne-bids... to be done later I guess

Originally posted by @agramfort in #980 (review)

cc @larsoner

[larsoner]

Adding a scraper for plot_alignment or other things that just use a simple 3D scene is as simple as adding 'image_scrapers': ('pyvista', ...) to sphinx_gallery-conf in principle. In practice you then need to make sure it actually renders properly.

If you want stc.plot or something, you want _BrainScraper or so, but it's still doable.

I'd wait until you had a use case, then I'm happy to help. It sounds like you can't actually use it for #980 because you don't have the right files (?).

[sappelhoff]

Do we still need this? Where are we missing a 3D figure in our docs?

This was the example worked on in #980: https://mne.tools/mne-bids/stable/auto_examples/convert_ieeg_to_bids.html#sphx-glr-auto-examples-convert-ieeg-to-bids-py

looks fine to me? I'd close this issue.