Add an internal API to ListenOptions to determine if an endpoint is configured to use HTTPS. This is a temporary as the design of connection adapters and configuration will churn before release.
- Put everything in the libuv transport package under `Microsoft.AspNetCore.Server.Kestrel.Transport.Libuv.*` namespaces.
- Move stuff in Transport.Libuv/Internal/Http and Transport.Libuv/Internal/Infrastructure to Transport.Libuv/Internal (keep the Networking directory for the libuv wrappers).
- Add `Libuv` prefix to most libuv internal classes.
- Rename `KestrelEngine` to `LibuvTransport`.
- Rename `SocketOutputConsumer` to `LibuvOutputConsumer`.
- Rename `SocketOutputProducer` to `OutputProducer`.
- Fix namespaces in `Microsoft.AspNetCore.Server.Kestrel.Core.`