Cleanup: use 'BKE_' prefix for BKE_deform API calls

- Use 'BKE_object_defgroup' prefix for object functions.

- Rename 'defvert_verify_index' to 'defvert_ensure_index'
  since this adds the group if it isn't found.

source/blender/makesrna/intern/rna_particle.c

@@ -1396,7 +1396,7 @@ static void psys_vg_name_set__internal(PointerRNA *ptr, const char *value, int i
     psys->vgroup[index] = 0;
   }
   else {
-    int defgrp_index = defgroup_name_index(ob, value);
+    int defgrp_index = BKE_object_defgroup_name_index(ob, value);
 
     if (defgrp_index == -1) {
       return;