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/bedlevel/abl/G29.cpp

@@ -498,7 +498,7 @@ G29_TYPE GcodeSuite::G29() {
       set_bed_leveling_enabled(abl_should_enable);
       g29_in_progress = false;
       #if ENABLED(LCD_BED_LEVELING)
-        lcd_wait_for_move = false;
+        ui.wait_for_bl_move = false;
       #endif
     }
 
@@ -790,7 +790,7 @@ G29_TYPE GcodeSuite::G29() {
   #if ENABLED(PROBE_MANUALLY)
     g29_in_progress = false;
     #if ENABLED(LCD_BED_LEVELING)
-      lcd_wait_for_move = false;
+      ui.wait_for_bl_move = false;
     #endif
   #endif