Check for UDFPS finger down for face auth device entry

Previously any successful face-auth triggered from touching
the udfps area would result in the user entering the device.
Instead, check that the finger is down on success to proceed
to device entry.

Test: atest SystemUITests
Fixes: 233213741
Bug: 195161518
Change-Id: Ie7a2fb034cfb811022771b16494d2bea71058459