This implements the `Apply Modifier` operator for GPv3.
Applies the modifier to the current frame. Drawings at the current frame will be updated.
If the result of the modifier creates new layers, the layers will be added and a drawing
at the current frame will be inserted.
Applying a modifier will run the following steps:
* Create a localized copy of the original Grease Pencil data and insert it into a geometry
set that owns it.
* Execute the `modifiy_geometry_set` function of the modifier with this geometry set.
* In the resulting Grease Pencil data loop over all layers:
* If the original data has a layer with the same name, overwrite its drawing data in the
current frame.
* Otherwise create a new layer in the original data and insert a resulting drawing at
the current frame.
* Remove all original layers that are not mapped to from a result layer.
* Remap the material indices for all drawings that have not been updated (e.g. the ones
that are not on the current frame).
* Copy all the layer attributes to the original Grease Pencil.
Pull Request: https://projects.blender.org/blender/blender/pulls/124543
81d78e3416