Move OnBackInvokedCallback to window package.

Originally, View was implementing onBackInvokedDisptacherOwner, but now
only Activity and Dialog and since back event are related to the
window, it makes sense to move them into the android.window package

This follow up comment at:
ag/c/platform/frameworks/base/+/16764116/comments/e131f3ef_e3e1d2e0

Test: atest BackNavigationTests
Bug: 221401221
Change-Id: Ia2f26162beb6a41b6e162b31e599e882f8bf7320