patch 8.1.2350: other text for CTRL-V in Insert mode with modifyOtherKeys

Problem:    Other text for CTRL-V in Insert mode with modifyOtherKeys.
Solution:   Convert the Escape sequence back to key as if modifyOtherKeys is
            not set, and use CTRL-SHIFT-V to get the Escape sequence itself.
            (closes #5254)
diff --git a/src/proto/edit.pro b/src/proto/edit.pro
index bc69b41..49b9f4c 100644
--- a/src/proto/edit.pro
+++ b/src/proto/edit.pro
@@ -2,6 +2,7 @@
 int edit(int cmdchar, int startln, long count);
 int ins_need_undo_get(void);
 void ins_redraw(int ready);
+int decodeModifyOtherKeys(int c);
 void edit_putchar(int c, int highlight);
 char_u *prompt_text(void);
 int prompt_curpos_editable(void);