Add DPM API to explicitly set/get global restrictions

Changed the existing setUserRestriction API to set restrictions locally
on the calling user or parent user, and migrated user restrictions to
the policy engine.

Bug: 232918480
Bug: 258442475
Test: btest -sw android.devicepolicy.cts.UserRestrictionsTest
Change-Id: Icdedc0e9311fb8efcae2f7e5aaf480ea7a900a78