Add list of approved services in addApprovedList

... instead of replacing it. I.e., do what the method name claims to do
in order to fix restoring. Otherwise during restore the list of
components is getting set to the list of the components from backup set,
i.e., list of pre-approved components is lost.

This is ag/3939056 in master.

Bug: 77630371
Test: with a backup set for package "android" created with LocalTransport run (also see the bug) adb root && adb shell bmgr enable true && adb shell bmgr transport android/com.android.internal.backup.LocalTransport && adb shell bmgr backupnow android && adb shell rm -rf /cache/backup/1/_delta/android/ && adb push android /cache/backup/1/_delta/ && adb shell cat /data/system/notification_policy.xml | grep enabled_listeners -C 5 && adb shell bmgr restore 1 android && adb shell cat /data/system/notification_policy.xml | grep enabled_listeners -C 5
Test: atest FrameworksUiServicesTests
Change-Id: Ie0eb6ef6629fb4c6d97f06b891282aa3e5563456