[flexiglass] Multiple input method bouncer scene.

Expanded the placeholder bouncer scene to correctly show different UIs
based on the authentication method and call the correct auth APIs to
check user input, unlock the device, etc.

Bug: 280877228
Test: unit tests included. Manually tested with the entire relation
chain in the Compose Gallery testdbed app.

Change-Id: I1dff6dc1d849fd0b3d5d5dff300485e3ef770f08