Make setRemoteAdapter() work for nested RemoteViews

This change adds applyNestedView() and reapplyNestedView() to
RemoteViews. This makes it possible to pass the top-level
"rootParent" view (usually AppWidgetHostView for widgets) to nested
RemoteViews that are added by addView(). This allows setRemoteAdapter
actions to work properly when they are used in nested RemoteViews.

Bug: 214288099
Test: RemoteViewsTest
Change-Id: I4fa3fe98d89bffdc0a5be46dabed12b9c217219e