Mark KeyframeEffect.p.iterationComposite experimental (#10270)
Mark KeyframeEffect.p.iterationComposite experimental (#10270)

https://developer.mozilla.org/en-US/docs/Web/API/KeyframeEffect/iterationComposite
has an Experimental banner, and https://drafts.csswg.org/web-animations-2/#dom-keyframeeffect-iterationcomposite
has a persistent overlay with this message:

> Not Ready For Implementation
>
> This spec is not yet ready for implementation. It exists in this
> repository to record the ideas and promote discussion.

Related: https://github.com/w3c/browser-specs/issues/279#issuecomment-831123224
chrisdavidmills/browser-compat-data,mdn/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data