Set initialExpandedChildrenCount dynamically in location settings

In location settings, we want "Advanced" button show up right after "App
level permissions". But with different numbers of "recent location requests" apps,
the Preferences hidden under Advanced could change.

To fix this issue, we fetch the list of apps with "recent location
requests" in LocationSettings.onCreate(), and set
initialExpandedChildrenCount for location PreferenceScreen to the apps
count.

Bug: 70350519
Test: Manual
Change-Id: I4c4b6bdfa916213494a29e8ae8b5f33476411c88