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/term.pro b/src/proto/term.pro
index 5af1996..8f1d33c 100644
--- a/src/proto/term.pro
+++ b/src/proto/term.pro
@@ -65,6 +65,7 @@
 void del_termcode(char_u *name);
 void set_mouse_topline(win_T *wp);
 int is_mouse_topline(win_T *wp);
+int decode_modifiers(int n);
 int check_termcode(int max_offset, char_u *buf, int bufsize, int *buflen);
 void term_get_fg_color(char_u *r, char_u *g, char_u *b);
 void term_get_bg_color(char_u *r, char_u *g, char_u *b);