Use EnforcingAdmin on RestrictedPreferenceHelper

This patch adds methods to use the EnforcingAdmin class in
RestrictedPreferenceHelper and RestrictedLockUtils. It will allow to use
new DevicePolicyManager API (added in ag/34058536) to get enforcing
admin in follow-up changes.

This change also exposes EnforcingAdmin::getComponentName() method to
allow RestrictedLockUtils to access it. Previously, it was an hidden
API.

Flag: android.app.admin.flags.policy_transparency_refactor_enabled
Flag: android.app.admin.flags.enforcing_admin_get_component_name_enabled
Bug: 414733570
FCRS_CODE : mcolh0glw6rmhp
Test: atest RestrictedLockUtilsTest
Test: atest RestrictedPreferenceHelperTest

Change-Id: I39ba376d27231f0285575862b8ef44aa7ebb9c7b