Root-level blocking wheel listeners still need to disable async wheel
routing globally, but non-root listeners only block the regions where
their event path can cancel the wheel event. The previous routing
admission treated any blocking listener as global, which prevented
async scrolling in unaffected nested scrollports.
Base routing admission on viewport-covering blocking regions instead of
the presence of any blocking listener, leaving local blocker rejection
to the compositor hit test. Update internals so blocked positions report
no async wheel target. Update the admission test to cover the routing
distinction and add a nested scroller test where a non-passive wheel
listener calls preventDefault(), keeping both the scroller and the
viewport at their original offsets.
1687a955d3