Add a new keyframe type named 'generated', which is meant to indicate
that the key was set by some automated tool (like an add-on), rather
than manually by an animator.
This is meant for tooling that needs to create keys in a repeatable way.
With this new key type, the tool can know which keys it generated
before, and thus those can be removed and re-generated.
Pull Request: https://projects.blender.org/blender/blender/pulls/120564
51e1f29a68
