Armature deformation modifier for Grease Pencil v3.
Changes compared to GPv2:
- `multi` DNA field was unused and was removed.
- `vert_coords_prev` array is unused and was removed (gets passed to
armature functions but never gets allocated).
- GPv3 modifier uses the common `influence` struct to store the vertex
group name, for consistency. The
`GREASE_PENCIL_INFLUENCE_INVERT_VERTEX_GROUP` flag is copied to
`deformflag` as `ARM_DEF_INVERT_VGROUP` before evaluation, which is
used internally by armature functions.
- `BKE_armature_deform_coords_with_curves` is added as another variant
of the deform function, but uses C++ parameter types (spans instead
of raw pointers). It gets a `Span<MDeformVert>` directly instead of
deducing it internally from the object type. This is because we want
to do this curve-by-curve and already use arbitrary vector spans for
positions.
Pull Request: https://projects.blender.org/blender/blender/pulls/118752
5599172499