Fix: Scale/Rotate proportional editing for Grease Pencil / Curves

If the `transdata_check_local_islands` check does not succeed, we end up
with `CTX_NO_PET` for scaling/rotation.

For `Grease Pencil`, this was lost in the transition from GPv2 > GPv3
(type was renamed to "legacy", then removed from
`transdata_check_local_islands` in a804320138, but the new type was
never added).

Curves never specified support for this, but both types are (in theory)
taking into account `V3D_AROUND_LOCAL_ORIGINS` in
`curve_populate_trans_data_structs` (logic from 9d86fada03 might be a
bit broken for proportional editing "islands" without anything selected
as reported in #139101, but that will be corrected in another PR).

So to resolve, add `Grease Pencil` and `Curves` as supported object
types in `transdata_check_local_islands`

NOTE: `transdata_check_local_center` already has these two types as
well.

Part of #139101

Pull Request: https://projects.blender.org/blender/blender/pulls/139209

source/blender/editors/transform/transform.cc

@@ -78,7 +78,8 @@ bool transdata_check_local_islands(TransInfo *t, short around)
   if (t->options & (CTX_CURSOR | CTX_TEXTURE_SPACE)) {
     return false;
   }
-  return ((around == V3D_AROUND_LOCAL_ORIGINS) && ELEM(t->obedit_type, OB_MESH));
+  return ((around == V3D_AROUND_LOCAL_ORIGINS) &&
+          ELEM(t->obedit_type, OB_MESH, OB_GREASE_PENCIL, OB_CURVES));
 }
 
 /** \} */