patch 8.1.1988: :startinsert! does not work the same way as "A"

Problem:    :startinsert! does not work the same way as "A".
Solution:   Use the same code to move the cursor. (closes #4896)
diff --git a/src/proto/normal.pro b/src/proto/normal.pro
index cc4bf7d..dd62226 100644
--- a/src/proto/normal.pro
+++ b/src/proto/normal.pro
@@ -23,4 +23,5 @@
 int get_visual_text(cmdarg_T *cap, char_u **pp, int *lenp);
 void start_selection(void);
 void may_start_select(int c);
+void set_cursor_for_append_to_line(void);
 /* vim: set ft=c : */