Make style updates reach a fixed point when slot invalidation dirties
assigned nodes after their traversal point. During inherited-style
cascades, only the topmost changed element scans for descendant slots.
Animation inherited-style updates now include the target slot and walk
shadow-including descendants, so host animations propagate inherited
values through shadow trees and assigned slottables. Animated inherited
longhands also carry the same inherited-style invalidation signal as
regular style changes.
Mark custom elements dirty when their :defined state flips, so upgraded
elements do not keep stale :not(:defined) computed style. Add coverage
for slotted menu invalidation, descendant-slot scan counts, target slot
animations, host shadow-tree animations, and explicit inherit from an
animated non-inherited longhand.
CustomStateSet directly selected the style invalidation reason used when
its JS-visible set is modified. Move that mapping into
CSS::Invalidation::CustomElementInvalidator.
This keeps the custom-state container focused on its set contents while
CSS invalidation owns the style work required by :state() selectors.
Element.cpp still spelled out the :defined pseudo-class invalidation set
when custom element state changed. Move that selector policy into
CustomElementInvalidator.
This keeps Element responsible for the state transition, while
CSS::Invalidation owns the affected selector feature.
