Demix GlobalEventHandlers; adapt to new events structure

[queengooborg]

This PR performs two operations relating to the GlobalEventHandlers mixin.

First, the mixin is de-mixed and separated into their individual interfaces. This includes Document, Window, HTMLElement,
MathMLElement, and SVGElement.

Second, the event handlers are converted to the new naming convention, and URLs are also updated. In the process, duplicates are removed.

Possible conflict with #15677.

[foolip]

I think that for the most part these should be a single event entry, and it needs to be decided on a case-by-case basis. Some should be multiple entries still, a few events like "blur" can be fired at both Window and some elements and have different meanings for those.

There are far too many events to do this in batch and review the result properly, I suggest splitting into many small PRs.

[foolip]

This entry isn't meaningful, no event will ever be fired for document.addEventListener('canplay', handler) because the event target is an HTMLMediaElement and the events doesn't bubble.

[Elchi3]

Right now we have:
https://developer.mozilla.org/en-US/docs/Web/API/GlobalEventHandlers/oncanplay
https://developer.mozilla.org/en-US/docs/web/api/htmlmediaelement/canplay_event

Per IDL, it would be possible to have the event on:
Window
Document
HTMLElement
MathMLElement
SVGElement

I wonder if we wouldn't be better off if we have the events under GlobalEventHandlers in BCD. On MDN we also place them under GlobalEventHandlers and document where they are available (list above) and where they are typically used (in this case HTMLMediaElements like video and audio). What do you think?

[queengooborg]

I'm marking this as a draft because there is some inaccurate flag data in this mixin that I'd like to get removed first before this is merged.

[Elchi3]

There are far too many events to do this in batch and review the result properly, I suggest splitting into many small PRs.

Agree. I think we should close this PR and work our way through GlobalEventHandlers piece by piece. However, I would suggest to open one or two PRs for the moment that deal with one or two events only. Then we can play through what updates we want to make exactly in BCD and also on MDN for these events. Once we are clear, we can open a lot more PRs given we then know what we're doing.

[queengooborg]

I'm going to close this PR and create other PRs for each individual event instead, so that each one can be reviewed individually.