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/msg.cpp.em

@@ -77,7 +77,7 @@ topic_fields = ["%s %s" % (convert_type(field.type, True), field.name) for field
 constexpr char __orb_@(name_snake_case)_fields[] = "@( ";".join(topic_fields) );";
 
 @[for topic in topics]@
-ORB_DEFINE(@topic, struct @uorb_struct, @(struct_size-padding_end_size), __orb_@(name_snake_case)_fields, static_cast<uint8_t>(ORB_ID::@topic));
+ORB_DEFINE(@topic, struct @uorb_struct, @(struct_size-padding_end_size), __orb_@(name_snake_case)_fields, static_cast<orb_id_size_t>(ORB_ID::@topic));
 @[end for]
 
 void print_message(const orb_metadata *meta, const @uorb_struct& message)

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)];
 }

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

@@ -62,7 +62,7 @@ static constexpr size_t orb_topics_count() { return ORB_TOPICS_COUNT; }
  */
 extern const struct orb_metadata *const *orb_get_topics() __EXPORT;
 
-enum class ORB_ID : uint8_t {
+enum class ORB_ID : orb_id_size_t {
 @[for idx, topic_name in enumerate(topic_names_all)]@
 	@(topic_name) = @(idx),
 @[end for]