uorb: allow for more than 255 uORB messages

Increased size for ORB_ID from uint8_t to uint16_t

Created a type: orb_id_size_t = uint16_t.
There are still a couple of places where the size
of the ORB_ID is assumed to be less than 16-bits.
The places that I have found are commented regarding
this and can be found with a search on orb_id_size_t.

Tools/msg/templates/uorb/uORBTopics.cpp.em

@@ -76,5 +76,5 @@ const struct orb_metadata *get_orb_meta(ORB_ID id)
 		return nullptr;
 	}
 
-	return uorb_topics_list[static_cast<uint8_t>(id)];
+	return uorb_topics_list[static_cast<orb_id_size_t>(id)];
 }