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/gcode/control/M999.cpp

@@ -38,7 +38,7 @@
  */
 void GcodeSuite::M999() {
   Running = true;
-  lcd_reset_alert_level();
+  ui.reset_alert_level();
 
   if (parser.boolval('S')) return;