Run apex_sepolicy_tests

.. as a validation for apex.

apex_sepolicy_tests checks the contents of the apex against
precompilec_sepolicy. This is to avoid common mistakes in file_contexts.
For example, etc/vintf directory should be read-able by servicemanager.

Bug: 267269895
Test: m com.google.cf.wifi (with wrong file_contexts entry)
Change-Id: Ic363345df43e5b2108b07de787f5f6817bbe6af4