HTTP/3: Consider adding new connection feature for completing or pooling stream

`QuicStreamContext.DisposeAsync()` is used to:

1. Wait for the connection to drain
2. Call back to `Http3Stream` and notify it that the stream is complete
3. Optionally pool the context
4. Dispose `QuicStream`.

Consider adding an `ICompleteConnectionFeature` or `IConnectionDrainFeature` that handles step 1. That would allow step 2 to happen without a callback.

Benefits:
1. Reduce the amount of logic in `DisposeAsync()`
2. Performance benefit of not registering and executing callback for each request.

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Alternatively, add a feature that is explicitly for pooling the QUIC stream back onto the QUIC connection.