BackupManagerService: Make new behavior conditional on ChangeId.

Base CL ag/12885739 introduced unconditional enforcement of the BACKUP
permission for callers of BackupManagerService.isBackupServiceActive()
in the service, but dropped the enforcement on the app process side
(BackupManager).

This CL makes the behavior change conditional on a compat ChangeId.

Bug: 158482162
Test: Manually checked that an app similar to the code sample from
      http://b/158482162#comment1 can reproduce the behavior.
      This is true both before the base CL and after this CL, when
      the app targets an old SDK version (26).
Test: Checked that both (a) before this CL, (b) after this CL where
      the change is manually enabled for the app via the below commands,
      the app runs into a SecurityException instead:
$ adb shell am compat enable 158482162 com.example.tester
$ adb shell dumpsys platform_compat | grep 158482162
ChangeId(158482162; name=IS_BACKUP_SERVICE_ACTIVE_ENFORCE_PERMISSION_IN_SERVICE; enableSinceTargetSdk=31; packageOverrides={com.example.tester=true})

Change-Id: I58e5d2a0b438296137fd76720636c8fdce740ded
Merged-In: I58e5d2a0b438296137fd76720636c8fdce740ded
(cherry picked from commit 7671f0d9)