16/n: Introduce ClientMonitor#FinishCallback

The main purpose of this CL is to decouple ClientMonitor's "finishing"
from the onError, onAcquired, onAuthenticated, etc callback handlers.
This will allow us to eventually move all operations into ClientMonitor
subclasses (think generateChallenge, revokeChallenge, etc which are
synchronous).

We can then introduce a scheduler to ensure __all__ HAL operations are
performed serially, not just the current ClientMonitor implementations.

Bug: 157790417

However, since things are still a bit intertwined, a few additional
changes are also necessary.

1) Added FinishCallback - All ClientMonitors are responsible for
   invoking this callback, notifying its owner that the current
   operation is complete
2) Added Cancellable - only Authenticate, Enroll (in other words,
   AcquisitionClient subclasses) are cancellable. Remainder of
   operations are "system" things and should never be canceled. In
   addition, the current HIDL contract is vague as to what the expected
   behavior would be if cancel() was invoked while one of the other
   operations are in process
3) Added ErrorConsumer - only Authenticate, Enroll (in other words,
   AcquisitionClient subclasses) receive onError from the HAL

This change should be functionally equivalent, except the following:
1) onError is now only applicable to Authenticate, Enroll
2) Cancel is now only applicable to Authenticate, Enroll

Test: On fingerprint and face devices, do the following:
      1) Internal cleanup (unknown framework template, unknown HAL
         template) by modifying Fingerprint/FaceUtils
      2) Enroll
      3) Lockout on fingerprint/face devices
      4) Auth (lockscreen, BiometricPrompt) success/reject
      5) Remove templates from settings

Change-Id: Icce99dbdb0aa076bc1dddd3f3c9ea74d4960df93