quic: reset rejected HTTP/3 request streams with H3_REQUEST_REJECTED #65441

When an incoming HTTP/3 request stream is rejected without any application processing (e.g. the session has no consumer for it), we destroy the stream but don't reset it with H3_REQUEST_REJECTED.

RFC 9114 §4.1.1:

When the server cancels a request without performing any application processing, the request is considered "rejected". The server SHOULD abort its response stream with the error code H3_REQUEST_REJECTED.

That code is the signal that the server did not process the request at all. Without it, the client can't distinguish an unprocessed request from one we may have acted on.

First raised as a follow-up on #64192 (comment).