Cleanup: keyframe API naming, high level keyframe API

- Split 'verify_fcurve' into two functions:

  ED_action_fcurve_ensure which adds the f-curve if needed.
  ED_action_fcurve_find which returns NULL when not found.

  Callers of ED_action_fcurve_find had unused 'group'
  argument which has been removed.

- Rename verify_adt_action to ED_id_action_ensure

  It had an argument to add data which was always true,
  remove this instead of splitting in into a separate function.

source/blender/python/intern/bpy_rna_anim.c

@@ -502,7 +502,7 @@ PyObject *pyrna_struct_keyframe_delete(BPy_StructRNA *self, PyObject *args, PyOb
     BKE_reports_init(&reports, RPT_STORE);
 
     result = delete_keyframe(
-        G.main, &reports, (ID *)self->ptr.owner_id, NULL, group_name, path_full, index, cfra, 0);
+        G.main, &reports, (ID *)self->ptr.owner_id, NULL, path_full, index, cfra, 0);
     MEM_freeN((void *)path_full);
 
     if (BPy_reports_to_error(&reports, PyExc_RuntimeError, true) == -1) {