Edit activity for hub mode

- enter edit mode by tapping the edit icon
- edit mode requires keyguard unlocking
- adding and removing widgets are only enabled in edit mode

Test: atest CommunalInteractorTest
Bug: 309968801
Fix: 309968801
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Change-Id: I210d4ae035e570b8b9d135b7b17d86d1f1ce436c