Unify toast presentation code

Extract window layout construction and view inflation from Toast and
ToastUI into common @hide class ToastPresenter. This is desirable by
itself but also in preparation for making system toasts visible to all
users.

Bug: 149408635
Test: atest ToastUITest android.widget.cts.ToastTest
      android.widget.cts29.ToastTest android.server.wm.ToastTest

Change-Id: Ifdd7ee37687da2e4c7abed61569cf342f95b2611