Cleanup Event and EventTarget

[kitsonk]

This PR does a couple things:

• Refactors Event and EventTarget so that they better encapsulate their non-public data as well as are more forward compatible with things like DOM Nodes.
• Moves dom_types.ts -> dom_types.d.ts which was always the intention, it was a legacy of when we used to build the types from the code and the limitations of the compiler. There was a lot of cruft in dom_types which shouldn't have been there, and mis-alignment to the DOM standards. This generally has been eliminated, though we still have some minor differences from the DOM (like the removal of some deprecated methods/properties).
• Adds DOMException. Strictly it shouldn't inherit from Error, but most browsers provide a stack trace when one is thrown, so the behaviour in Deno actually better matches the browser.

Event still doesn't log to console like it does in the browser. I wanted to get this raised and that could be an enhancement later on (it currently doesn't either).

[ry]

This file contains a ton of overlap with cli/js/lib.deno.shared_globals.d.ts is there some way this code can be shared?

[kitsonk]

Let me think about it. It is a valid point, and it is slowly killing us by a thousand papercuts.

[kitsonk]

Ok, I found a way... For things that are part of this PR (Event, EventTarget, CustomEvent, and DOMException) I have eliminated them from dom_types and instead am just using lib.deno.shared_globals.d.ts. I would recommending doing the rest as a subsequent PR. It does take a little bit of effort to make sure you get it right. Take a look at the last commit in isolation to get an idea of what I had to do.

[ry]

LGTM - great clean up! I'm really glad you found a way to share types with lib.deno.shared_globals.d.ts. It seems there are a lot of other types that we can now eliminate from cli/js/web/dom_types.d.ts, but I agree this should be done later.