Make items selectable in the communal hub

This change makes items in the hub selectable by tapping on them. Once
an item is selected, it can also be removed by tapping on the remove
button. Tapping elsewhere on the screen will unselect the item or select
another one.

Test: flashed and verified changes on-device by selecting/unselecting
items
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Bug: 318537189

Change-Id: I62bef163e1b94d26b7fe1b5aa60ce619351dade6