Adds object conversion between Grease Pencil and Curves types.
GPv3 object is converted to Curves by combining all visible layers at
the current frame.
Curves object is converted to Grease Pencil by constructing a new layer
and keyframe with the curves geometry.
The type enum for the conversion operator gets a dynamic function to
check for the experimental flags and only show the enabled Grease Pencil
object types. It does not currently exclude unsupported type
combinations.
Pull Request: https://projects.blender.org/blender/blender/pulls/122304
f5b9ff15a0