Use 16-bit ride_id_t thoughout and raise RIDE_ID_NULL (#14411)

* Replace RIDE_ENTRY_INDEX_NULL with OBJECT_ENTRY_INDEX_NULL

Ride entries are objects like any other, so there is little point having separate constants.

* Use ride_id_t in many more places

* Change RIDE_ID_NULL to 0xFFFF

* Increment network version

* Update replays

Co-authored-by: duncanspumpkin <duncans_pumpkin@hotmail.co.uk>

src/openrct2/world/Footpath.cpp

@@ -572,7 +572,7 @@ struct rct_neighbour
 {
     uint8_t order;
     uint8_t direction;
-    uint8_t ride_index;
+    ride_id_t ride_index;
     uint8_t entrance_index;
 };