feat(blender): Add new Blender conversion API

Taken from !474 (closed). It's extremely unclear to me how to split up that branch cleanly (as in, having nicer, self-contained commits without all the exploratory stuff). For the time being, I will continue to use it as an experimental branch, split off changes into separate MRs (such as this one) and merge it back into !474 (closed). Eventually, everything will be split off and !474 (closed) will be redundant.

TODO:

• switch to row representation
• tests (suggestion: refactor and extend examples/blender/docs/new_api.py, in particular, periodic curves are missing; there might be more) @samy @tyburn (as per zulip)
• users guide entry (suggestion: use examples/blender/docs/new_api.py with literalinclude and such)
• images for user guide
• api docs @hoekstra if you'd like
• deal with homogenise (couldn't use ddg.math.projective.homogenize, because it isn't vectorised...), leave this to different MR relating to vectorisation
• figure out where the functions should live and better names
• the bmesh_transformation parameter to ifs_to_blender should perhaps be removed, because it would fit neatly into mesh_transformation as well, see !511 (merged). Done in !516 (merged)