Update PhoneWindow to new window inset dispatching

PhoneWindow was relying on an implementation detail of the
old fitSystemWindow mechanism to consume only the top inset.
In the new mechanism, the contract changed an consuming the
inset did no longer work, leading to the insets being applied
twice in some cases.

Bug: 15388544
Change-Id: Ife8361f2b1e5caf8c3ed90646344d653876e8e7d