Fixes and additions to VDM unit tests

- Fix flag usage in VirtualDeviceTest
- Fix a typo in VirtualDeviceManagerTest
- Add GenericWindowPolicyControllerTest to test GWPC in isolation.
  Contains a modified copy of test cases from VDMSTest to only account
for GWPC.
- Add tests for GWPC policy to block permission dialogs
- Add tests in VirtualDeviceManagerServiceTest to ensure the permission
  flag behaves as expected.

Bug: 298032672
Bug: 291737919
Test: atest com.android.server.companion.virtual
Change-Id: I79b54aee75b05c60ca84490f10a23e5bee04ed3f