Implementation of the extrude operator for Grease Pencil v3.
If an endpoint is selected, the extrusion will extend the stroke.
If an inner point is selected, the extrusion will create a new stroke tied to the one that is selected.
Change of behavior from gpv2: the endpoints of a cyclic curve follow the same behavior as inner points.
Pull Request: https://projects.blender.org/blender/blender/pulls/121249
725408e842