Adds x and y to IntersectionObserverEntry

[mhassan1]

This PR adds x and y to all instances of IntersectionObserverEntry in the IntersectionObserver polyfill.

Resolves #116.

[JakeChampion]

/ok-to-test sha=15a5742

https://github.com/Financial-Times/polyfill-library/actions/runs/2834150336

[romainmenke]

https://developer.mozilla.org/en-US/docs/Web/API/DOMRectReadOnly

DOMRectReadOnly.top Read only
Returns the top coordinate value of the DOMRect (usually the same as y.)

When is it not the same?

https://drafts.fxtf.org/geometry/#DOMRect

The y attribute, on getting, it must return the y coordinate value. For the DOMRect interface, setting the y attribute must set the y coordinate to the new value.

The top attribute, on getting, must return the NaN-safe minimum of the y coordinate and the sum of the y coordinate and the height dimension.

Is it correct that y can be NaN-unsafe and top can not?

[mhassan1]

y is different from top when height is negative; for example,

{
  y: 10
  top: 9
  height: -1
}

In the case of this polyfill, it doesn't seem like height will ever be negative, so they will always be the same.

I'm not sure if any of the top values in this polyfill could ever be NaN, but if they could, what would we use for y, since y is derived from top?

[romainmenke]

I agree that the difference won't matter in the context of this polyfill.
Thank you for helping me understand it better :)

[romainmenke]

LGTM! Thank you 🎉