libdvr: Add performance API to platform library.

- Add dvrPerformanceSetSchedulerPolicy API. Only this API is exposed
  through the DVR platform library, the older API will be deprecated.
- Add permission checks to all performanced APIs.
- Allow services with android.permission.RESTRICTED_VR_ACCESS to change
  scheduler policy for VR apps.
- Minor updates to use the updated PDX service API. The older API will
  be deprecated soon.
- Add tests for permission checks and policy API.

Most of the tests are automatic however, there is one manual step for
testing the android.permission.RESTRICTED_VR_ACCESS (e.g. trusted uid)
check. Because there is no reliable way to determine the UID of VrCore
from the gtest, instead the gtest looks for an env var named
GTEST_TRUSTED_UID; if this is set the value is used as a uid and the
trusted uid tests are enabled.

Bug: 62468109
Test: 'GTEST_TRUSTED_UID=<VrCore UID> performance_service_tests' passes.
Change-Id: I9047b298a015a69535b655a299ca26c179e2d57d