DevicePolicyManagerService - migrate to platform compat framework gating.

Replace targetSDK check with platform compat framework gating for admin password changes in R.
Define a new change id and use it for gating the change.

Test: com.android.cts.devicepolicy.MixedDeviceOwnerTest#testResetPasswordWithToken
Test: com.android.cts.devicepolicy.DeviceAdminHostSideTestApi23#testRunDeviceOwnerPasswordTest
Test: com.android.cts.devicepolicy.MixedDeviceOwnerTestApi25#testPasswordRequirementsApi
Bug: 123562444
Change-Id: Icf2515a0ade1fb7bf60d22b7c705346a2d75acba