This PR updates the socket transport code to swap between a Node web
socket transport or a web one based on the `isNode` environment. It also
adds unit tests to the browser tests that show we can connect in a
browser.
This commit creates a test that runs in the browser and ensures that we
can instantiate a pptr Connection with a fake transport and send/receive
messages.
Longer term I'd like to have tests that actually connect to a browser
and send CDP messages but that needs some changes to web-test-runner
which I'm going to speak to them about - the DevTools URL needs to be
exposed some how for us to use and connect to.
