Previously, adding or removing a constructed `CSSStyleSheet` via
`document.adoptedStyleSheets` invalidated style for the entire document
or shadow root. We now route this through the same style invalidation
machinery that's used when we add or remove `<style>` elements,
resulting in fewer full invalidations.
AdoptedStyleSheets.cpp still handled CSS-side fallout from adopted sheet
list mutations directly. Move sheet attachment and media-query setup to
a CSS invalidation helper, along with rule-cache invalidation.
The observable array callbacks continue to validate JS values and
same-document construction rules. The helper now owns the CSS work for
when a constructed stylesheet becomes visible to, or is removed from, a
Document or ShadowRoot.
