Extruder: Add g-code to set extruder step_distance (#2598)

Signed off by: David Smith <davidosmith@gmail.com>

klippy/stepper.py

@@ -94,6 +94,10 @@ class MCU_stepper:
         return self._oid
     def get_step_dist(self):
         return self._step_dist
+    def set_step_dist(self, sk, dist):
+        self._step_dist = dist
+        self.set_stepper_kinematics(sk)
+        logging.info("%s manually set to =%.6f", (self._name, dist))
     def is_dir_inverted(self):
         return self._invert_dir
     def calc_position_from_coord(self, coord):