patch 9.0.1209: getting interface member does not always work
Problem: Getting interface member does not always work.
Solution: Convert the index on the interface to the index on the object.
(closes #11825)
diff --git a/src/proto/vim9class.pro b/src/proto/vim9class.pro
index 35485ed..74d33c0 100644
--- a/src/proto/vim9class.pro
+++ b/src/proto/vim9class.pro
@@ -1,4 +1,5 @@
/* vim9class.c */
+int object_index_from_itf_index(class_T *itf, int idx, class_T *cl);
void ex_class(exarg_T *eap);
type_T *class_member_type(class_T *cl, char_u *name, char_u *name_end, int *member_idx);
void ex_enum(exarg_T *eap);