Accessibility updates for UDFPS device entry

Adds a UDFPS a11y overlay on the lockscreen that takes
up the bottom half of the screen. If there are hover
events over this area when touchExploration is enabled,
there will be a11y announcements guiding the user to
the UDFPS sensor.

This CL integrates this functionality on the lockscreen
only and does not yet support the alternate bouncer.

Updates Kosmos & testing.

Flag: NONE
Bug: 310044681
Test: atest UdfpsAccessibilityOverlayViewModelTest
Change-Id: I9b5f680edc9901ba4c06bdecccef0bac7b1cb424