Disable communal hub if lockscreen widgets are disabled

This change refactors out the logic determining whether communal is
enabled or disabled into a separate interactor/repository. It also adds
logic to check for DevicePolicyManager disabling lockscreen widgets.

Bug: 323196422
Test: atest SystemUiRoboTests
Flag: ACONFIG com.android.systemui.communal_hub STAGING
Change-Id: I96b1d909271201c45f9d4a29e039644fa71ccd6e