* MouseRegion documentation claimed that onEnter and onExit
would track entry and exit regardless of whether the pointer was
down or up
* It did such, but when grabbing the value of `event.down` from
the passed event, the value was always `false`
* PointerEnterEvent and PointerExitEvent were overriding the value
passed from PointerEvent in constructors, even if the value was true
e.g. in invocations of .fromMouseEvent((PointerMoveEvent...))
* This change now passes the value along to PointerEnter/ExitEvents
while providing it a default of false, and updates documentation
Fixes#40637
034358e341