Make recoverablekeystore use LockscreenCredential instead of (type, bytes)

Passing raw credential type values and byte arrays around is
error-prone.  Instead, just use LockscreenCredential which is for
exactly that purpose.

Some of the unit tests used invalid credentials that cannot actually be
represented by LockscreenCredential and therefore don't occur in the
real system.  For the unit tests that used invalid patterns (containing
bytes other than digits 1-9), update them to use valid patterns.  Remove
the unit test run_customLockScreen_RecoveryStatusFailure(), since the
type system prevents that case from being reachable anymore.

To keep the unit tests run_setsCorrectSnapshotVersion() and
run_recreatesMissingSnapshot() passing, I also replaced the first call
to KeySyncTask#run() in them with KeySyncTask#syncKeys() directly.  This
was necessary because the second call to KeySyncTask#run() would
otherwise occur after the KeySyncTask's credential was already zeroized.
Before, it worked by accident.  After this change, an exception gets
thrown from LockscreenCredential#ensureNotZeroized().  Note that this
change in behavior does not affect the non-test code, since it never
calls run() multiple times on the same KeySyncTask.

Bug: 431226484
Test: atest FrameworksServicesTests:com.android.server.locksettings
Flag: EXEMPT refactor
Change-Id: I2ea19109abe3fc30ffbccba94013b47b449ef27c