BioPasskeys UI Bugfix to use DisplayName

The get flow was generated with a 'username' bit to account for general
flows, but the passkey flow needs to condition to use displayname where
possible. That conditioning needs to also be done in the biometric
handler when the credential entry is being read.

Bug: 333445772
Test: E2E AndroidVault Test
Flag: EXEMPT bugfix
Change-Id: I6036ef8581cfc573528e4bbe42b3d5e728db365b