More explicit handling for end-of-group bit

The previous "implicit" end of group handling both created additional malformed track cases, and was challenging to integrate into existing MoQ APIs.  Change the interpretation to mean it's the same as receiving an End of Group Object with ID + 1.

Fixes: #1093

Author: afrind

draft-ietf-moq-transport.md

@@ -3234,8 +3234,18 @@ There are 8 defined Type values for OBJECT_DATAGRAM:
 | 0x07 | Yes           | Yes        | No        |
 |------|---------------|------------|-----------|
 
-For Type values where End of Group is Yes, the Object is the last Object in the
-Group.
+For Type values where End of Group is Yes, the effect is the same as receiving
+the current Datagram followed by an OBJECT_DATAGRAM_STATUS with the following
+values:
+
+~~~
+  Track Alias = datagram.Track Alias
+  Group ID = datagram.Group ID
+  Object ID = datagram.Object ID + 1
+  Publisher Priority = datagram.Publisher Priority
+  Extension Headers Length = 0
+  Object Status = End of Group
+~~~
 
 For Type values where Extensions Present is No, Extensions Headers Length is not
 present and the Object has no extensions.  When Extensions Present is Yes,
@@ -3361,10 +3371,20 @@ There are 12 defined Type values for SUBGROUP_HEADER:
 | 0x1D | Yes           | N/A             | Yes        | Yes          |
 |------|---------------|-----------------|------------|--------------|
 
-For Type values where Contains End of Group is Yes, the last Object in this
-Subgroup stream before a FIN is the last Object in the Group.  If the Subgroup
-stream is terminated with a RESET_STREAM or RESET_STREAM_AT, the receiver cannot
-determine the End of Group Object ID.
+For Type values where Contains End of Group is Yes, when the Subgroup stream is
+terminated with a FIN, the effect is the same as receiving an additional Object
+in the Subgroup with the following values:
+
+~~~
+  Object ID Delta = 0
+  Extension Headers Length = 0
+  Object Payload Length = 0
+  Object Status = End of Group
+~~~
+
+If such a Subgroup stream is terminated with a RESET_STREAM or RESET_STREAM_AT,
+no End of Group object can be inferred.  If the stream contains no Objects,
+Object 0 is the End of Group.
 
 For Type values where Subgroup ID Field Present is No, there is no explicit
 Subgroup ID field in the header and the Subgroup ID is either 0 (for Types