Misc. improvements (#12747)

* Make ExtUI respect MAXTEMP limits
  - Temperatures are now clamped by MAXTEMP limits rather than arbitrary values.
* Speed up USB init, add status
  - Speed up USB initialization
  - Show status message if init failed
* Enable status messages for EXTENSIBLE_UI
* Adjust max limit to MAX_TEMP - 15
* Misc. tweaks to formatting, const, etc.

Marlin/src/module/motion.cpp

@@ -47,7 +47,7 @@
   #include "../feature/bedlevel/bedlevel.h"
 #endif
 
-#if HAS_AXIS_UNHOMED_ERR && ENABLED(ULTRA_LCD)
+#if HAS_AXIS_UNHOMED_ERR && (ENABLED(ULTRA_LCD) || ENABLED(EXTENSIBLE_UI))
   #include "../lcd/ultralcd.h"
 #endif
 
@@ -1019,7 +1019,7 @@ void prepare_move_to_destination() {
       if (zz) SERIAL_ECHOPGM(MSG_Z);
       SERIAL_ECHOLNPGM(" " MSG_FIRST);
 
-      #if ENABLED(ULTRA_LCD)
+      #if ENABLED(ULTRA_LCD) || ENABLED(EXTENSIBLE_UI)
         ui.status_printf_P(0, PSTR(MSG_HOME " %s%s%s " MSG_FIRST), xx ? MSG_X : "", yy ? MSG_Y : "", zz ? MSG_Z : "");
       #endif
       return true;

Marlin/src/module/temperature.cpp

@@ -2470,7 +2470,7 @@ void Temperature::isr() {
 
   #endif // AUTO_REPORT_TEMPERATURES
 
-  #if ENABLED(ULTRA_LCD)
+  #if ENABLED(ULTRA_LCD) || ENABLED(EXTENSIBLE_UI)
     void Temperature::set_heating_message(const uint8_t e) {
       const bool heating = isHeatingHotend(e);
       #if HOTENDS > 1

Marlin/src/module/tool_change.cpp

@@ -681,7 +681,7 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
           singlenozzle_temp[active_extruder] = thermalManager.target_temperature[0];
           if (singlenozzle_temp[tmp_extruder] && singlenozzle_temp[tmp_extruder] != singlenozzle_temp[active_extruder]) {
             thermalManager.setTargetHotend(singlenozzle_temp[tmp_extruder], 0);
-            #if ENABLED(ULTRA_LCD)
+            #if ENABLED(ULTRA_LCD) || ENABLED(EXTENSIBLE_UI)
               thermalManager.set_heating_message(0);
             #endif
             (void)thermalManager.wait_for_hotend(0, false);  // Wait for heating or cooling