Add screensaver home control setting

This setting controls whether home controls are visible on the
screensaver

Bug: 271330583
Test: verified setting correctly disables/enables button
Test: make -j64 RunSettingsLibRoboTests ROBOTEST_FILTER="com.android.settingslib.dream.DreamBackendTest"
Test: atest ComplicationTypesUpdaterTest
Change-Id: I44e0e8c4f81984604f4b47489b91f07285c75e15