"create an event" actually needs to take a timestamp

[annevk]

The current description

the time of the occurrence that the event is signaling

is rather handwavy and doesn't make sense for all callers (e.g., document.createEvent()). Updating all the callsites is tricky though.

[annevk]

I think we should make type an argument as well. I guess that means realm can no longer be optional though., but that doesn't seem too bad.