Fix and optimize case-light code

Marlin/Marlin_main.cpp

   #endif
 }
 
-#if HAS_CASE_LIGHT
-
-  void setup_case_light() {
-    digitalWrite(CASE_LIGHT_PIN,
-      #if ENABLED(CASE_LIGHT_DEFAULT_ON)
-        255
-      #else
-        0
-      #endif
-    );
-    analogWrite(CASE_LIGHT_PIN,
-      #if ENABLED(CASE_LIGHT_DEFAULT_ON)
-        255
-      #else
-        0
-      #endif
-    );
-  }
-
-#endif
-
 void setup_powerhold() {
   #if HAS_SUICIDE
     OUT_WRITE(SUICIDE_PIN, HIGH);
 
 #if HAS_CASE_LIGHT
 
+  uint8_t case_light_brightness = 255;
+
+  void update_case_light() {
+    digitalWrite(CASE_LIGHT_PIN, case_light_on ? HIGH : LOW);
+    analogWrite(CASE_LIGHT_PIN, case_light_on ? case_light_brightness : 0);
+  }
+
   /**
    * M355: Turn case lights on/off and set brightness
    *
    *   P<byte>  Set case light brightness (PWM pin required)
    */
   inline void gcode_M355() {
-    static uint8_t case_light_brightness = 255;
     if (code_seen('P')) case_light_brightness = code_value_byte();
-    if (code_seen('S')) {
-      case_light_on = code_value_bool();
-      digitalWrite(CASE_LIGHT_PIN, case_light_on ? HIGH : LOW);
-      analogWrite(CASE_LIGHT_PIN, case_light_on ? case_light_brightness : 0);
-    }
+    if (code_seen('S')) case_light_on = code_value_bool();
+    update_case_light();
     SERIAL_ECHO_START;
     SERIAL_ECHOPGM("Case lights ");
     case_light_on ? SERIAL_ECHOLNPGM("on") : SERIAL_ECHOLNPGM("off");
   #endif
 
   #if HAS_CASE_LIGHT
-    setup_case_light();
+    update_case_light();
   #endif
 
   #if HAS_BED_PROBE

Marlin/ultralcd.cpp

   #if HAS_POWER_SWITCH
     extern bool powersupply;
   #endif
-  #if HAS_CASE_LIGHT
-    extern bool case_light_on;
-  #endif
+
   const float manual_feedrate_mm_m[] = MANUAL_FEEDRATE;
   void lcd_main_menu();
   void lcd_tune_menu();
 
   #endif //SDSUPPORT
 
+  #if HAS_CASE_LIGHT && ENABLED(MENU_ITEM_CASE_LIGHT)
+
+    extern bool case_light_on;
+    extern void update_case_light();
+
+    void toggle_case_light() {
+      case_light_on = !case_light_on;
+      lcdDrawUpdate = LCDVIEW_CALL_REDRAW_NEXT;
+      update_case_light();
+    }
+
+  #endif // MENU_ITEM_CASE_LIGHT
+
   /**
    *
    * "Main" menu
     // Switch case light on/off
     //
     #if HAS_CASE_LIGHT && ENABLED(MENU_ITEM_CASE_LIGHT)
-      if (case_light_on == 0)
-        MENU_ITEM(gcode, MSG_LIGHTS_ON, PSTR("M355 S1"));
+      if (case_light_on)
+        MENU_ITEM(function, MSG_LIGHTS_OFF, toggle_case_light);
       else
-        MENU_ITEM(gcode, MSG_LIGHTS_OFF, PSTR("M355 S0"));
+        MENU_ITEM(function, MSG_LIGHTS_ON, toggle_case_light);
     #endif
 
     #if ENABLED(BLTOUCH)