🚸 Default T0 for M569, M906, M913 (#23020)

Marlin/src/gcode/feature/L6470/M906.cpp

 
       #if E_STEPPERS
         case E_AXIS: {
-          const int8_t target_e_stepper = get_target_e_stepper_from_command();
+          const int8_t target_e_stepper = get_target_e_stepper_from_command(0);
           if (target_e_stepper < 0) return;
           switch (target_e_stepper) {
             #if AXIS_IS_L64XX(E0)

Marlin/src/gcode/feature/trinamic/M569.cpp

  */
 void GcodeSuite::M569() {
   if (parser.seen('S'))
-    set_stealth_status(parser.value_bool(), get_target_e_stepper_from_command());
+    set_stealth_status(parser.value_bool(), get_target_e_stepper_from_command(0));
   else
     say_stealth_status();
 }

Marlin/src/gcode/feature/trinamic/M906.cpp

 
       #if E_STEPPERS
         case E_AXIS: {
-          const int8_t target_e_stepper = get_target_e_stepper_from_command();
+          const int8_t target_e_stepper = get_target_e_stepper_from_command(0);
           if (target_e_stepper < 0) return;
           switch (target_e_stepper) {
             #if AXIS_IS_TMC(E0)

Marlin/src/gcode/feature/trinamic/M911-M914.cpp

           break;
         #if E_STEPPERS
           case E_AXIS: {
-            const int8_t target_e_stepper = get_target_e_stepper_from_command();
+            const int8_t target_e_stepper = get_target_e_stepper_from_command(0);
             if (target_e_stepper < 0) return;
             switch (target_e_stepper) {
               TERN_(E0_HAS_STEALTHCHOP, case 0: TMC_SET_PWMTHRS_E(0); break;)

Marlin/src/gcode/gcode.cpp

 }
 
 /**
- * Get the target e stepper from the T parameter
- * Return -1 if the T parameter is out of range or unspecified
+ * Get the target E stepper from the 'T' parameter.
+ * If there is no 'T' parameter then dval will be substituted.
+ * Returns -1 if the resulting E stepper index is out of range.
  */
-int8_t GcodeSuite::get_target_e_stepper_from_command() {
-  const int8_t e = parser.intval('T', -1);
+int8_t GcodeSuite::get_target_e_stepper_from_command(const int8_t dval/*=-1*/) {
+  const int8_t e = parser.intval('T', dval);
   if (WITHIN(e, 0, E_STEPPERS - 1)) return e;
 
   SERIAL_ECHO_START();

Marlin/src/gcode/gcode.h

   static void say_units();
 
   static int8_t get_target_extruder_from_command();
-  static int8_t get_target_e_stepper_from_command();
+  static int8_t get_target_e_stepper_from_command(const int8_t dval=-1);
   static void get_destination_from_command();
 
   static void process_parsed_command(const bool no_ok=false);