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/M17_M18_M84.cpp

@@ -63,7 +63,7 @@ void GcodeSuite::M18_M84() {
     #if HAS_LCD_MENU && ENABLED(AUTO_BED_LEVELING_UBL)
       if (ubl.lcd_map_control) {
         ubl.lcd_map_control = false;
-        set_defer_return_to_status(false);
+        ui.defer_status_screen(false);
       }
     #endif
   }

Marlin/src/gcode/control/M80_M81.cpp

@@ -83,7 +83,7 @@
     #endif
 
     #if HAS_LCD_MENU
-      lcd_reset_status();
+      ui.reset_status();
     #endif
   }
 

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;