Refactor BKE_id_copy_ex to return the new ID pointer.

Note that possibility to pass the new ID pointer as parameter was kept,
as this is needed for some rather specific cases (like in depsgraph/COW,
when copying into already allocated memory).

Part of T71219.

source/blender/editors/physics/particle_object.c

@@ -754,7 +754,7 @@ static bool remap_hair_emitter(Depsgraph *depsgraph,
     return false;
   }
   /* don't modify the original vertices */
-  BKE_id_copy_ex(NULL, &mesh->id, (ID **)&mesh, LIB_ID_COPY_LOCALIZE);
+  mesh = (Mesh *)BKE_id_copy_ex(NULL, &mesh->id, NULL, LIB_ID_COPY_LOCALIZE);
 
   /* BMESH_ONLY, deform dm may not have tessface */
   BKE_mesh_tessface_ensure(mesh);