Adds scrollsnapchange and scrollsnapchanging event support

[argyleink]

1. https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollsnapchange_event
2. https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollsnapchanging_event

[rschristian]

Thanks!

The main branch is targetting v11, which is still in beta. If you're willing to mirror this to the v10.x branch, targetting the current v10 release line, we'd appreciate it, else one of us will do it when we can.

[coveralls]

coverage: 99.442%. remained the same
when pulling 00fd3ea on argyleink:scrollsnapchange-scrollsnapchanging-events
into 6241a5a on preactjs:main.

Shouldn't have approved

[argyleink]

The main branch is targetting v11, which is still in beta. If you're willing to mirror this to the v10.x branch, targetting the current v10 release line, we'd appreciate it, else one of us will do it when we can.

mirror into v10.x #4947

[rschristian]

Hope you don't mind, I just went ahead and added the corrections to your branch as I realized TS hasn't yet shipped SnapEvent (or hasn't in our version, anyhow) and it'd require a bit of wrangling to set up. Not a lot of work, but equally, not something we'd expect for folks with 0 context of this repo.

Thanks again!