Homing backoff per-axis / delta Z (#14789)

Marlin/src/gcode/calibrate/G28.cpp

 
   #endif // DUAL_X_CARRIAGE
 
-  #ifdef HOMING_BACKOFF_MM
-    endstops.enable(false);
-    constexpr float endstop_backoff[XYZ] = HOMING_BACKOFF_MM;
-    const float backoff_x = doX ? ABS(endstop_backoff[X_AXIS]) * (X_HOME_DIR) : 0,
-                backoff_y = doY ? ABS(endstop_backoff[Y_AXIS]) * (Y_HOME_DIR) : 0,
-                backoff_z = doZ ? ABS(endstop_backoff[Z_AXIS]) * (Z_HOME_DIR) : 0;
-    if (backoff_z) do_blocking_move_to_z(current_position[Z_AXIS] - backoff_z);
-    if (backoff_x || backoff_y) do_blocking_move_to_xy(current_position[X_AXIS] - backoff_x, current_position[Y_AXIS] - backoff_y);
-  #endif
   endstops.not_homing();
 
   #if BOTH(DELTA, DELTA_HOME_TO_SAFE_ZONE)

Marlin/src/module/motion.cpp

 void do_blocking_move_to_x(const float &rx, const float &fr_mm_s/*=0.0*/) {
   do_blocking_move_to(rx, current_position[Y_AXIS], current_position[Z_AXIS], fr_mm_s);
 }
+void do_blocking_move_to_y(const float &ry, const float &fr_mm_s/*=0.0*/) {
+  do_blocking_move_to(current_position[Y_AXIS], ry, current_position[Z_AXIS], fr_mm_s);
+}
 void do_blocking_move_to_z(const float &rz, const float &fr_mm_s/*=0.0*/) {
   do_blocking_move_to(current_position[X_AXIS], current_position[Y_AXIS], rz, fr_mm_s);
 }
     if (axis == Z_AXIS && STOW_PROBE()) return;
   #endif
 
+  #ifdef HOMING_BACKOFF_MM
+    constexpr float endstop_backoff[XYZ] = HOMING_BACKOFF_MM;
+    const AxisEnum backoff_mm = endstop_backoff[
+      #if ENABLED(DELTA)
+        Z_AXIS
+      #else
+        axis
+      #endif
+    ];
+    if (backoff_mm) {
+      current_position[axis] -= ABS(backoff_mm) * axis_home_dir;
+      line_to_current_position();
+    }
+  #endif
+
   // Clear retracted status if homing the Z axis
   #if ENABLED(FWRETRACT)
     if (axis == Z_AXIS) fwretract.current_hop = 0.0;

Marlin/src/module/motion.h

  */
 void do_blocking_move_to(const float rx, const float ry, const float rz, const float &fr_mm_s=0);
 void do_blocking_move_to_x(const float &rx, const float &fr_mm_s=0);
+void do_blocking_move_to_y(const float &ry, const float &fr_mm_s=0);
 void do_blocking_move_to_z(const float &rz, const float &fr_mm_s=0);
 void do_blocking_move_to_xy(const float &rx, const float &ry, const float &fr_mm_s=0);