8/n: Schedule invalidation request

This should happen 1) Upon successful enrollment, and 2) After
session creation, if the framework detects a previous invalidation
has not completed for some reason.

Note that invalidation only needs to be requested if the (sensor, user)
pair has enrollments.

Also fixes the case where no sensors require invalidation.

Test: atest com.android.server.biometrics
Test: atest CtsBiometricsTestCases, existing tests pass. Additional
      tests will be added in a subsequent CL.
Bug: 159667191
Change-Id: Id14391370904df004380428f1a064224489e2898