Add WS root span option

[scott-rc]

This adds a way to make WS <event> spans become root spans that link back to their original parent.

Examples

Make WS open spans be root:

const socket = withWSOpenRoot(() => new WebSocket("wss://echo.websocket.org"));

Make WS open and WS close spans be root:

let socket;
withWSOpenRoot(() => {
	withWSCloseRoot() => {
		socket = new WebSocket("wss://echo.websocket.org");
	});
});