Reconfigure Scoped Storage experiment: force ScSt on list of apps

Add a DeviceConfig feature that denotes a list of apps we want to force
into scoped storage. This would allow us to test these apps behaviours
under scoped storage at scale.

Also add the feature to StorageManagerService#dump.

Test: manual:
$ adb shell device_config put storage_native_boot forced_scoped_storage_whitelist <pkg>
$ adb reboot
$ adb shell dumpsys appops --package <pkg> # observe LEGACY_STORAGE
mode=ignored
Test: adb shell dumpsys mount
Bug: 151735608

Change-Id: I6a43e987ebf8d14fb64103a74bafde28f5863ae2