feat(wt_video): implement cursor position

[TheButlah]

Extends the functionality of the demo to include streamed control inputs, such as the location of the mouse. This is accomplished by introducing a new unidirectional stream from the browser to the server. This byte-oriented reliable stream is framed using tokio-util's framing mechanism, specifically the length delimited framing. This converts the AsyncRead into an async Stream<Item=Bytes>. Then, we use tokio-serde to convert that stream to a Stream<Item=MyEnum>, where the bytes are deserialized as json using serde. Finally we introduce a select statement in the server to dispatch the different events to their respective event handlers.