Use PromptKind to decide which layout to show.

1. Update PromptKind and use it to decide which layout to show.
In this way, we could know what PromptKind is before rendering the
layout. This enables us to use PromptKind to decide show one-pane or
two-pane layout as a follow-up step.

2. Do some clean ups.

Test: atest PromptSelectorInteractorImplTest
Test: atest PromptViewModelTest
Bug: 330908557
Flag: ACONFIG android.hardware.biometrics.custom_biometric_prompt NEXTFOOD

Change-Id: I2facb1e722c9f58475de92d685deddb3df055270