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/getchar.pro b/src/proto/getchar.pro
index cfb3ab4..0e24bd3 100644
--- a/src/proto/getchar.pro
+++ b/src/proto/getchar.pro
@@ -37,6 +37,7 @@
 void close_all_scripts(void);
 int using_script(void);
 void before_blocking(void);
+int merge_modifyOtherKeys(int c_arg);
 int vgetc(void);
 int safe_vgetc(void);
 int plain_vgetc(void);