Fix switching extruder

`DONT_SWITCH` got lost along the way. Replace it with `DO_SWITCH_EXTRUDER` and adjust the code.

Marlin/src/Marlin.cpp

   #include "feature/fanmux.h"
 #endif
 
-#if (ENABLED(SWITCHING_EXTRUDER) && !DONT_SWITCH) || ENABLED(SWITCHING_NOZZLE) || ENABLED(PARKING_EXTRUDER)
+#if DO_SWITCH_EXTRUDER || ENABLED(SWITCHING_NOZZLE) || ENABLED(PARKING_EXTRUDER)
   #include "module/tool_change.h"
 #endif
 
     setup_endstop_interrupts();
   #endif
 
-  #if ENABLED(SWITCHING_EXTRUDER) && !DONT_SWITCH
+  #if DO_SWITCH_EXTRUDER
     move_extruder_servo(0);  // Initialize extruder servo
   #endif
 

Marlin/src/gcode/config/M218.cpp

  *   T<tool>
  *   X<xoffset>
  *   Y<yoffset>
- *   Z<zoffset> - Available with DUAL_X_CARRIAGE and SWITCHING_NOZZLE
+ *   Z<zoffset> - Available with DUAL_X_CARRIAGE, SWITCHING_NOZZLE and PARKING_EXTRUDER
  */
 void GcodeSuite::M218() {
   if (get_target_extruder_from_command() || target_extruder == 0) return;

Marlin/src/inc/Conditionals_LCD.h

   #define E_MANUAL        EXTRUDERS
 #endif
 
+#define DO_SWITCH_EXTRUDER (ENABLED(SWITCHING_EXTRUDER) && (DISABLED(SWITCHING_NOZZLE) || SWITCHING_EXTRUDER_SERVO_NR != SWITCHING_NOZZLE_SERVO_NR))
+
 /**
  * DISTINCT_E_FACTORS affects how some E factors are accessed
  */

Marlin/src/lcd/ultralcd.cpp

     else
       MENU_ITEM(gcode, MSG_AUTO_HOME, PSTR("G28"));
 
-    #if ENABLED(SWITCHING_EXTRUDER)
+    #if ENABLED(SWITCHING_EXTRUDER) || ENABLED(SWITCHING_NOZZLE)
 
       #if EXTRUDERS == 4
         switch (active_extruder) {

Marlin/src/module/configuration_store.cpp

         SERIAL_ECHOPAIR_P(port, "  M218 T", (int)e);
         SERIAL_ECHOPAIR_P(port, " X", LINEAR_UNIT(hotend_offset[X_AXIS][e]));
         SERIAL_ECHOPAIR_P(port, " Y", LINEAR_UNIT(hotend_offset[Y_AXIS][e]));
-        #if ENABLED(DUAL_X_CARRIAGE) || ENABLED(SWITCHING_NOZZLE) ||ENABLED(PARKING_EXTRUDER)
+        #if ENABLED(DUAL_X_CARRIAGE) || ENABLED(SWITCHING_NOZZLE) || ENABLED(PARKING_EXTRUDER)
           SERIAL_ECHOPAIR_P(port, " Z", LINEAR_UNIT(hotend_offset[Z_AXIS][e]));
         #endif
         SERIAL_EOL_P(port);

Marlin/src/module/tool_change.cpp

   #include "../feature/fanmux.h"
 #endif
 
-#if ENABLED(SWITCHING_EXTRUDER)
+#if DO_SWITCH_EXTRUDER
 
   #if EXTRUDERS > 3
     #define REQ_ANGLES 4
 
 #endif // DUAL_X_CARRIAGE
 
-#define DO_SWITCH_EXTRUDER (SWITCHING_EXTRUDER_SERVO_NR != SWITCHING_NOZZLE_SERVO_NR)
-
 /**
  * Perform a tool-change, which may result in moving the
  * previous tool out of the way and the new tool into place.

Marlin/src/module/tool_change.h

 
 #include "../inc/MarlinConfig.h"
 
-#if ENABLED(SWITCHING_EXTRUDER)
+#if DO_SWITCH_EXTRUDER
   void move_extruder_servo(const uint8_t e);
 #endif