Encapsulate common display code in a singleton (#12395)

* Encapsulate common LCD code in a singleton
* Depend more UBL code on UBL_DEVEL_DEBUGGING
  - Since most users don't need the debugging on at all times, this helps reduce the default build size for UBL by over 2K, a little closer to fitting on 128K boards.

Marlin/src/lcd/menu/menu_custom.cpp

@@ -40,10 +40,10 @@
 void _lcd_user_gcode(PGM_P const cmd) {
   enqueue_and_echo_commands_P(cmd);
   #if ENABLED(USER_SCRIPT_AUDIBLE_FEEDBACK)
-    lcd_completion_feedback();
+    ui.completion_feedback();
   #endif
   #if ENABLED(USER_SCRIPT_RETURN)
-    lcd_return_to_status();
+    ui.return_to_status();
   #endif
 }