Finalize BiometricPrompt Strings

Dependent on recent discussions, caused by a modality discussion and a
discussion on the nullability of provider input, this CL aims to
finalize and polish all the strings for the BiometricPrompt flow.

Bug: 330396140
Test: Build and video tests
Change-Id: I983d626363c4ff59fcf8d84ad27b6680d0f0e2c6