Support touchExplorationEnabled on udfps

- When touchExplorationEnabled, touch events become hover events. This
updates UdfpsController to handle hover events so the user can still
authenticate when a11y options are enabled
- Update UdfpsView contentDescription
- Update LockIconViewController labels to support a11y

Test: manual
Bug: 185912108
Change-Id: Ic9590607105459506f8ce5d4d73f779853f1ed31