Move some Stepper methods to Planner (#10719)

Marlin/planner.h

@@ -542,11 +542,27 @@ class Planner {
      */
     static void sync_from_steppers();
 
+    /**
+     * Get an axis position according to stepper position(s)
+     * For CORE machines apply translation from ABC to XYZ.
+     */
+    static float get_axis_position_mm(const AxisEnum axis);
+
+    // SCARA AB axes are in degrees, not mm
+    #if IS_SCARA
+      FORCE_INLINE static float get_axis_position_degrees(const AxisEnum axis) { return get_axis_position_mm(axis); }
+    #endif
+
     /**
      * Does the buffer have any blocks queued?
      */
     FORCE_INLINE static bool has_blocks_queued() { return (block_buffer_head != block_buffer_tail); }
 
+    //
+    // Block until all buffered steps are executed
+    //
+    static void synchronize();
+
     /**
      * "Discard" the block and "release" the memory.
      * Called when the current block is no longer needed.