Add Z_AFTER_HOMING to raise Z more in G28 (#16755)

Marlin/Configuration.h

@@ -1070,7 +1070,9 @@
 //#define UNKNOWN_Z_NO_RAISE      // Don't raise Z (lower the bed) if Z is "unknown." For beds that fall when Z is powered off.
 
 //#define Z_HOMING_HEIGHT  4      // (mm) Minimal Z height before homing (G28) for Z clearance above the bed, clamps, ...
-                             // Be sure you have this distance over your Z_MAX_POS in case.
+                                  // Be sure to have this much clearance over your Z_MAX_POS to prevent grinding.
+
+//#define Z_AFTER_HOMING  10      // (mm) Height to move to after homing Z
 
 // Direction of endstops when homing; 1=MAX, -1=MIN
 // :[-1,1]

Marlin/src/gcode/calibrate/G28.cpp

@@ -405,6 +405,7 @@ void GcodeSuite::G28(const bool always_home_all) {
 
     // Home Z last if homing towards the bed
     #if Z_HOME_DIR < 0
+
       if (doZ) {
         #if ENABLED(BLTOUCH)
           bltouch.init();
@@ -416,10 +417,17 @@ void GcodeSuite::G28(const bool always_home_all) {
         #endif
 
         #if HOMING_Z_WITH_PROBE && defined(Z_AFTER_PROBING)
+          #if Z_AFTER_HOMING > Z_AFTER_PROBING
+            do_blocking_move_to_z(Z_AFTER_HOMING);
+          #else
             probe.move_z_after_probing();
           #endif
+        #elif defined(Z_AFTER_HOMING)
+          do_blocking_move_to_z(Z_AFTER_HOMING);
+        #endif
 
       } // doZ
+
     #endif // Z_HOME_DIR < 0
 
     sync_plan_position();

Marlin/src/module/motion.cpp

@@ -1755,10 +1755,9 @@ void homeaxis(const AxisEnum axis) {
   #endif
 
   #if DISABLED(DELTA) && defined(HOMING_BACKOFF_MM)
-    constexpr xyz_float_t endstop_backoff = HOMING_BACKOFF_MM;
-    const float backoff_mm = endstop_backoff[axis];
-    if (backoff_mm) {
-      current_position[axis] -= ABS(backoff_mm) * axis_home_dir;
+    const xyz_float_t endstop_backoff = HOMING_BACKOFF_MM;
+    if (endstop_backoff[axis]) {
+      current_position[axis] -= ABS(endstop_backoff[axis]) * axis_home_dir;
       line_to_current_position(
         #if HOMING_Z_WITH_PROBE
           (axis == Z_AXIS) ? MMM_TO_MMS(Z_PROBE_SPEED_FAST) :