Implement js.lib.WeakRef

[dimensionscape]

WeakRef was introduced in ES2021 and is now supported on every major browser. I think it's time for Haxe to include it as well.

[haxiomic]

Minor tweak, maybe it's worth adding the constraint {}: class WeakRef<T: {}> as you can only have weak refs to objects and it's a runtime error to ref primitives like Int or String

WeakRef was introduced in ES2021 so it's quite new but still widely supported (~87% https://caniuse.com/?search=weakref) so I agree it's fair for it to be in js.lib

[dimensionscape]

Minor tweak, maybe it's worth adding the constraint {}: class WeakRef<T: {}> as you can only have weak refs to objects and it's a runtime error to ref primitives like Int or String

Absolutely correct. I actually didn't notice that I forgot to add the constraint when applying the Type param changes to my original commit. Thanks!

WeakRef was introduced in ES2021 so it's quite new but still widely supported (~87% https://caniuse.com/?search=weakref) so I agree it's fair for it to be in js.lib

Correct again. My apologies - I hadn't even had my morning coffee yet at the time of writing. Perhaps I was conflating with WeakMaps, but I'm not sure why I said ES6.

[haxiomic]

All good :], thank you for the contribution <3