Update the Python API documentation about crashes with multi-threaded
code.
- Move the "threading gotcha" into a file of its own. That way it's
immediately clear from looking at the Gotcha table of contents that
threading is not supported.
- Simplify the example code, so that it doesn't access `bpy`.
Apparently the problem is much wider than just multi-threaded access
to `bpy`, and involves _all_ Python threads, regardless of what they
do / access.
- Add some more explanation and move some text from the bottom to the
top, so that the first-read part (when reading top to bottom) has
most of the information.
Pull Request: https://projects.blender.org/blender/blender/pulls/139279
58d0b0e4b4