Jelle Raaijmakers 2f39b2dd63 LibWeb: Split shadow stylesheet host-side invalidation reach ...

Broad shadow-root stylesheet changes already restyle the whole shadow
tree, but host-side fallout does not always need a document-wide
invalidation. Split the host-side reach classification so selectors
contained to the host subtree, such as `:host *` and `:host > *`,
invalidate the host, while sibling-escaping selectors such as
`:host + :has(*)` still invalidate the host's root.

Recognize sibling escapes through positive selector-list pseudos such as
`:is()` and `:where()` as well, including selectors like
`:is(:host) + :has(*)` and `:is(:host + .item)`.

This avoids turning host-contained shadow stylesheet changes into full
document style invalidations. On https://pomax.github.io/bezierinfo/,
this reduces the time to produce a layout tree from about 8.7s to 3.6s
on my machine.

2026-05-05 18:36:34 +02:00

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