Summary:
When the application calls `stopSending` on an h3 WebTransport stream we sent
STOP_SENDING with `setReadCallback(id, nullptr, err)`, which also unregisters
the read callback. The peer's RESET_STREAM then never reached us, so
`WtStreamManager` never saw the ingress side close and never returned the
stream credit, and we never sent MAX_STREAMS. This uses `QuicSocket::stopSending`
instead, which sends STOP_SENDING and leaves the read callback in place. That
matches the http/2 path, which also waits for the peer's WT_RESET_STREAM before
reaping the read side.

Reviewed By: hanidamlaj

Differential Revision: D116105653

fbshipit-source-id: 90df54796a4c076fb0850ad11263de20699692a0