Rename directories to match their /tr counterpart.

With the exception of DOMEvents, domxpath, html which don't have unversioned /tr names for now.

This includes:

canvas2d -> 2dcontext
crypto-api -> WebCryptoAPI
DOMCore -> dom
PointerEvents -> pointerevents
ProgressEvents -> progress-events
SelectorsAPI -> selectors-api
ServerSentEvents -> eventsource
ShadowDOM -> shadow-dom
WebMessaging -> webmessaging
WebSockets -> websockets
WebStorage -> webstorage
Workers -> workers