More file-based encryption work.

Add granular StorageManager APIs for key creation/destruction and
unlocking/locking.  Start passing through an opaque token as part
of the unlock command, but leave it empty for now.  We now have a
separate "prepare" method that sanity checks that user directories
are correctly setup.

Define a handful of system properties used for marking devices that
should be operating in FBE mode, and if they're emulating FBE.  Wire
a command to "sm", but persisting will come later.

Start using new "encryptionAware" flag on apps previously marked with
coreApp flag, which were apps running in the legacy CryptKeeper
model.  Small tweaks to handle non-encryptionAware voice interaction
services.  Switch PackageManager to consult StorageManager about the
unlocked state of a user.

Bug: 22358539
Change-Id: Ic2865f9b81c10ea39369c441422f7427a3c3c3d6