itersolve: Add ability to query the active_flags state

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/stepper.py

@@ -165,6 +165,9 @@ class MCU_stepper:
                                              flush_time)
         if ret:
             raise error("Internal error in stepcompress")
+    def is_active_axis(self, axis):
+        return self._ffi_lib.itersolve_is_active_axis(
+            self._stepper_kinematics, axis)
 
 # Helper code to build a stepper object from a config section
 def PrinterStepper(config, units_in_radians=False):