Prompt for screen lock setup during private space unlock

This change introduces a dialog that enables the user to set up the
screen lock if it's not already enabled when they attempt to unlock a
private space.

Bug: 316129700
Test: atest PrivateSpaceAuthenticationActivityTest
Flag: android.multiuser.show_set_screen_lock_dialog

Change-Id: Iac3dd5762c0d082e3604df053873bb9195880991