Split up prepare_move by type

- For better encapsulation add inlines for each prepare_move type
- Move controllerFan vars inside the function as statics
- Some formatting cleanup
- Rename `ClearToSend` as `ok_to_send`

Marlin/Marlin.h

@@ -205,7 +205,7 @@ void enable_all_steppers();
 void disable_all_steppers();
 
 void FlushSerialRequestResend();
-void ClearToSend();
+void ok_to_send();
 
 void get_coordinates();
 #ifdef DELTA