Create a separate composable for integrating the bouncer in legacy keyguard.

This allows us to minor UI tweaks that are necessary for integrating the compose bouncer in legacy keyguard

Bug: 310005730
Flag: com.android.systemui.compose_bouncer
Test: everything builds, compose bouncer shows up when flag is on.
Change-Id: I4c7fb84250f187d1b31e8f3108b132caa2730240