Add selinux policy for the new Binder-based vr flinger vsync service.

Bug: 72890037

Test: - Manually confirmed that I can't bind to the new vsync service
from a normal Android application, and system processes (other than
vr_hwc) are prevented from connecting by selinux.

- Confirmed the CTS test
  android.security.cts.SELinuxHostTest#testAospServiceContexts, when
  built from the local source tree with this CL applied, passes.

- Confirmed the CTS test
  android.cts.security.SELinuxNeverallowRulesTest#testNeverallowRules521,
  when built from the local source tree with this CL applied, passes.

Change-Id: Ib7a6bfcb1c2ebe1051f3accc18b481be1b188b06