Add heating progress bars (#12543)

Marlin/src/lcd/ultralcd.cpp

@@ -257,6 +257,12 @@ void MarlinUI::init() {
   #if HAS_ENCODER_ACTION
     encoderDiff = 0;
   #endif
+
+  #if ENABLED(MARLIN_DEV_MODE)
+    // Start timer 5 at full speed
+    SET_CS(5, PRESCALER_1);
+    SET_COM(5, A, NORMAL);
+  #endif
 }
 
 bool MarlinUI::get_blink() {