The big keyguard transition refactor (5/n)

Also save surface for the home task, so unlocking to the homescreen
is as fast as before. Note that originally it was not possible to
save surface for home task because of artifacts when clicking the
home button. However, we added logic since then to disallow save
surface if it's a different intent, which is the case when pressing
the home button.

Also consolidate some relayout for less overhead.

Bug: 32057734
Change-Id: I53ede527cb1ff438001d4023ee3740283ee302ee