Update naming for the AlternateBouncer

Differentiate naming of the AlternateBouncer and
PrimaryBouncer. The AlternateBouncer was formerly
referred to as "AltAuth" and "AlternateAuth method".
Instead, consistently refer to it as the AlternateBouncer.
The AlternateBouncer can be implemented by specific
biometric modalities to encourage users to use a biometric
before the PrimaryBouncer (pin/pattern/password input) shows.

Test: atest SystemUITests
Bug: 237362467
Change-Id: Icd2f8fbf76192d9ce8b5ecad3aa4919f9c3a49c0