Update unpaused udfps alpha when showing udfps bouncer

This will make sure the alpha is updated correctly before
showing the udfps affordance.

This CL also updates the dumpsys to be more accurate of the
actual alpha value being used.

Test: manual, atest UdfpsKeyguardViewControllerTest
Bug: 197160246
Change-Id: I86a73dacfd2fc4f5b910e1e1e4f6535e91d00da3