On face auth success, verify the face auth'd user is the current user

Flag: EXEMPT BUGFIX
Bug: 463674813
Test: setup two users with one of them with
face enrolled, on user switching to the non-enrolled
face auth user, observe face auth doesn't unlock the device
Test: atest DeviceEntryFaceAuthRepositoryTest

(cherry picked from commit f09f1e9a96669af2c73125083c42f8c1cc3ed3c3)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:1cdd2deea0ac95bf8e039b7092e72bddb642e9f3
Merged-In: Ia006cf4220872208fc90fae293f63acbffdf4a66
Change-Id: Ia006cf4220872208fc90fae293f63acbffdf4a66