UI: Support UI operators with configurable shortcuts

After all a super simple solution that allows us to get rid of hardcoded keymap items.

source/blender/editors/interface/interface_ops.c

@@ -1185,8 +1185,6 @@ void ED_operatortypes_ui(void)
 
 /**
  * \brief User Interface Keymap
- *
- * For now only modal maps here, since UI uses special ui-handlers instead of operators.
  */
 void ED_keymap_ui(wmKeyConfig *keyconf)
 {

source/blender/editors/screen/area.c

@@ -1367,9 +1367,12 @@ static void region_subwindow(wmWindow *win, ARegion *ar, bool activate)
 static void ed_default_handlers(wmWindowManager *wm, ScrArea *sa, ListBase *handlers, int flag)
 {
 	/* note, add-handler checks if it already exists */
-	
+
 	/* XXX it would be good to have boundbox checks for some of these... */
 	if (flag & ED_KEYMAP_UI) {
+		wmKeyMap *keymap = WM_keymap_find(wm->defaultconf, "User Interface", 0, 0);
+		WM_event_add_keymap_handler(handlers, keymap);
+
 		/* user interface widgets */
 		UI_region_handlers_add(handlers);
 	}