patch 8.2.3788: lambda for option that is a function may be freed

Problem:    Lambda for option that is a function may be garbage collected.
Solution:   Set a reference in the funcref. (Yegappan Lakshmanan,
            closes #9330)
diff --git a/src/proto/insexpand.pro b/src/proto/insexpand.pro
index d455a98..6d97557 100644
--- a/src/proto/insexpand.pro
+++ b/src/proto/insexpand.pro
@@ -44,6 +44,7 @@
 int set_omnifunc_option(void);
 void set_buflocal_ofu_callback(buf_T *buf);
 int set_thesaurusfunc_option(void);
+int set_ref_in_insexpand_funcs(int copyID);
 callback_T *get_insert_callback(int type);
 void f_complete(typval_T *argvars, typval_T *rettv);
 void f_complete_add(typval_T *argvars, typval_T *rettv);