patch 8.2.5084: when the GUI shows a dialog tests get stuck

Problem:    When the GUI shows a dialog tests get stuck.
Solution:   Add the --gui-dialog-file argument.

src/proto/gui.pro

@@ -67,4 +67,5 @@ char_u *get_find_dialog_text(char_u *arg, int *wwordp, int *mcasep);
 int gui_do_findrepl(int flags, char_u *find_text, char_u *repl_text, int down);
 void gui_handle_drop(int x, int y, int_u modifiers, char_u **fnames, int count);
 int check_for_interrupt(int key, int modifiers_arg);
+int gui_dialog_log(char_u *title, char_u *message);
 /* vim: set ft=c : */

src/proto/main.pro

@@ -2,6 +2,7 @@
 int vim_main2(void);
 void common_init(mparm_T *paramp);
 int is_not_a_term(void);
+char_u *get_gui_dialog_file(void);
 int op_pending(void);
 void may_trigger_safestate(int safe);
 void state_no_longer_safe(char *reason);