Make DisplayDisconnectTransitionHandler an independent component.

Currently, DisplayDisconnectTransitionHandler only exists in
DesktopTasksController, meaning it only exists if the device supports
desktop mode. This causes test failures on devices that do not support
desktop since they do not create an instance of DesktopTasksController.

This CL fixes this by adding this transition handler as an independent
component, ensuring it's always built.

Bug: 365873835
Test: logcat on non-desktop device, confirm disconnect handler inits
Flag: com.android.window.flags.enable_display_disconnect_interaction
Change-Id: I81922aac7dcacd4cc143ab1d0a0834683d203356