Handle inline stylesheet @keyframes insertions without falling back to
broad owner invalidation. Recompute only elements whose computed
animation-name already references the inserted keyframes name.
Document-scoped insertions still walk the shadow-including tree so
existing shadow trees pick up inherited animations, and shadow-root
stylesheets fan out through the host root so :host combinators can
refresh host-side consumers as well. Also introduce the shared
ShadowRootStylesheetEffects analysis so later stylesheet mutation paths
can reuse the same per-scope escape classification.
