Desks: Deactivate active desk on Home task launch

Launching Home should close the active desktop session. When multiple
desks are enabled, this means the desk needs to be deactivated.

This fixes an issue where in CTS (where each test might launch Home
using adb) a prior test's desktop session might stay active causing
other tests to fail.

Flag: com.android.window.flags.enable_multiple_desktops_backend
Bug: 407602007
Test: atest ActivityLifecycleFreeformTests
Change-Id: I4d9c151b1f86c2907c78f32a26f3cd7dd4927e30