Allow the device policy management role to migrate accounts

Update copyAccountToUser to a SystemAPI

This is part of the work to split up the DevicePolicyManager
API createAndProvisionManagedProfile. The only caller of this
copyAccountToUser hidden SystemAPI will be the device policy
management role holder

Add permissions to gate the copyAccountToUser API and the
removeAccount API to allow the device policy management
role holder to call these APIs

Bug: 375382324
Test: atest AccountMigrationTest
Test: Manual testing by calling this SystemAPI in CloudDPC
 CTS tests will be added as a follow-up
Flag: android.app.admin.flags.split_create_managed_profile_enabled
Change-Id: I243f7ce53c6b8c8db1b946981895782f9d1c59dd