This is a partial revert of commit 82672089.
The previous commit removed a public type, which is a version-incompatible
change to the SELinux vendor API.  Since the 2017 devices are meant to be
launching with the previous version, this is unacceptable.  Revert the
version-incompatible parts of the change, but keep the other parts to enable
existing system functionality to persist and become part of MR1.  Leave TODOs
to remove the other parts when a version bump is acceptable.

Bug: 38241921
Test: Policy builds and device boots with ASAN enabled.
Change-Id: I0dd3673b8ed7fb86abd79cd04982396000e986f1