Introduce a +1234.56 format for over 999 steps/mm

Marlin/utility.h

@@ -63,6 +63,9 @@ void safe_delay(millis_t ms);
   // Convert signed float to string with +123.45 format
   char* ftostr52sign(const float& x);
 
+  // Convert signed float to string with +1234.56 format
+  char* ftostr62sign(const float& x);
+
   // Convert float to rj string with 123 or -12 format
   FORCE_INLINE char *ftostr3(const float& x) { return itostr3((int)x); }