Add new Factory reset protection policy APIs

Historically, FRP behaviour was built on top of the application restrictions
infrastructure. This CL introduces new behaviour, as the profile owner of an
organization-owned device needs to be able to control FRP behaviour and
cannot set application restrictions on user 0.

- Introduced a new FactoryResetProtectionPolicy object
  - Added it as a field to ActiveAdmin
  - Created a default value
- Added setFactoryResetProtectionPolicy to DPM which is used to set a
  factory reset protection policy. If the policy is null, the current
  policy is cleared and set back to the default value.
- Added getFactoryResetProtectionPolicy to DPM to retrieve the current
  factory reset protection policy. If this is the default value, then
  no policy is set.
- Both these APIs are callable by the device owner or profile owner of
  an organization-owned device.

Bug: 143517230
Test: atest com.android.server.devicepolicy.DevicePolicyManagerTest
      atest com.android.server.devicepolicy.FactoryResetProtectionPolicyTest
      atest com.android.cts.devicepolicy.MixedDeviceOwnerTest#testFactoryResetProtectionPolicy
      atest com.android.cts.devicepolicy.OrgOwnedProfileOwnerTest#testFactoryResetProtectionPolicy

Change-Id: I72c4d06ec8a27741a1956d082969573077937726