Blender Git Loki

Fix T93728: Greasepencil separate will loose all vertex groups

Caused by {rB3b6ee8cee708}

The raw data is copied here correctly
[`BKE_gpencil_stroke_weights_duplicate` in
`BKE_gpencil_stroke_duplicate`] but the vertex groups names are missing.
Prior to above commit is was enough to have `ED_object_add_duplicate`
(this seemingly took care of duplicating object's defbase).
Now vertex groups names sit on the `bGPdata` rather than the `Object`,
and since the separate operation creates **new** `bGPdata` we have to
copy vertex groups names - and active index - over [via
`BKE_defgroup_copy_list`].

Maniphest Tasks: T93728

Differential Revision: https://developer.blender.org/D13509