Cleanup: move Event.is_repeat & is_direction_inverted to flags

Use a flag for events to avoid adding struct members every time a new
kind of tag is needed - so events remain small.

This also simplifies copying settings as flags can be copied at once
with a mask.

source/blender/editors/interface/interface.c

@@ -6529,7 +6529,7 @@ void UI_but_focus_on_enter_event(wmWindow *win, uiBut *but)
 
   event.type = EVT_BUT_OPEN;
   event.val = KM_PRESS;
-  event.is_repeat = false;
+  event.flag = 0;
   event.customdata = but;
   event.customdata_free = false;