Add new Special App Access screen for Backup Tasks.

This new screen shows apps that hold the new RUN_BACKUP_JOBS permission.

Also add a reference to this screen in an app's info page under the
"Advanced" section for apps that have requested this permission.

Bug: 320563660
Test: BackupTasksAppsTest
Test: BackupTasksAppsPreferenceControllerTest
Test: visually via the Settings page

Change-Id: I7136fc74f3b0d0124889e7cf9e1234f917346432