Transfer the actual dispatcher when the window is preserved

When recreating the Activity, if the window is preserved,
onAttachedToWindow won't be called and PhoneWindow.onViewRootImplSet
won't be called either, where we set the actual dispatcher to the
Activiy's proxy dispatcher.

So when the window is preserved, we directly assign the actual Dispatcher
from the preserved Window to the new PhoneWindow

Fixes: 228571903
Test: In progress
Test: Open an app with OnBackInvokedCallback enabled, split to top,
      close the other application, do a back gesture
Change-Id: I050247501df8f6cf6cd0024a6233f88a035f6279