Don't hold old host callback for fragments on the back stack

LoaderManagers configure their host callback lazily as their
associated fragment is brought up through its lifecycle states. In the
case of fragments on the fragment back stack this could happen very
late, if at all. As a LoaderManager's host callback references the
host Activity, this means that a LoaderManager could keep a destroyed
Activity reference alive.

Update the host callbacks of all LoaderManagers eagerly during the
restore non-configuration instance phase.

Bug: 30653222
Test: core/tests/coretests/src/android/app/LoaderLifecycleTest.java
Change-Id: I5d2b81daae5e7cae429fcf4934e64b3ce281140c