This adds support for Overlay tests.
There are some differences with how we handle tests for other engines:
- The renders are captured using `bpy.ops.render.opengl()`, but this
won't work on our GPU build bots.
- A single blend file can run multiple tests by outputting a txt list
with the test names.
- Each overlay test blend file requires a matching script file with
the same name inside `tests/python/overlay/`.
- To reproduce a specific test state you can run
`blender "(...)/tests/data/overlay/<test>.blend" -P "(...)/tests/python/overlay/<test>.py" -- --test <test-number>`.
Note:
The current test permutations are WIP, so reference images are not
committed to the data repo for now.
Pull Request: https://projects.blender.org/blender/blender/pulls/133879
ba3749ad47