patch 8.2.4228: no tests for clicking in the GUI tabline

Problem:    No tests for clicking in the GUI tabline.
Solution:   Add test functions to generate the events.  Add tests using the
            functions. (Yegappan Lakshmanan, closes #9638)
diff --git a/src/proto/testing.pro b/src/proto/testing.pro
index 0d4ff49..b432b4f 100644
--- a/src/proto/testing.pro
+++ b/src/proto/testing.pro
@@ -35,6 +35,8 @@
 void f_test_scrollbar(typval_T *argvars, typval_T *rettv);
 void f_test_setmouse(typval_T *argvars, typval_T *rettv);
 void f_test_gui_mouse_event(typval_T *argvars, typval_T *rettv);
+void f_test_gui_tabline_event(typval_T *argvars, typval_T *rettv);
+void f_test_gui_tabmenu_event(typval_T *argvars, typval_T *rettv);
 void f_test_settime(typval_T *argvars, typval_T *rettv);
 void f_test_gui_drop_files(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */