Fix addAllowedPointer() overrides (#82834)

They should have been taking a PointerDownEvent.

This change was originally included in #81884, but that
had to be reverted because it broke Google testss. This
sub-part of that larger change needs to be made first in
order to allow for a phased rollout in a way that won't
break Google tests.

https://github.com/flutter/flutter/issues/81883