Add Event and requestAnimationFrame helpers and fix createBlob

[srujzs]

CustomEvents were handled specially in dart:html by jsifying compatible details and otherwise storing it on the side in variable. When accessing detail, it would check for this storage on the side first before directly returning the native detail. We could store it on the side here but that won't be symmetric with dart:html, so we leverage the native detail to store the object.

Event and KeyboardEvent constructors from dart:html have different defaults than the web, so that's reflected here as well.

requestAnimationFrame bound the current zone before, so there's a helper for that (mostly so users are aware that that is the equivalent member).

Lastly, createBlob should have been static so this fixes that.

[gemini-code-assist]

Code Review

This pull request introduces several extension methods and static helpers for DOM classes such as Blob, CustomEvent, Event, KeyboardEvent, and Window to ease migrations and compatibility. The review feedback highlights critical issues in the new extensions: a potential compile-time or runtime error in createCustomEvent due to unsafe handling of the nullable detail parameter, a logical bug in dartDetail where checking isA<JSAny?>() is always true and creates dead code, and a missing static keyword on createKeyboardEvent which prevents it from functioning as a constructor replacement helper.

[kevmoo]

We have some integration test bits. Any way to test these?

[srujzs]

We have some integration test bits. Any way to test these?

Yeah we should be a bit better about a lot of these helpers. I think the hope is they get removed eventually, but anyways, done!

[srujzs]

Thanks Kevin!