Re-fetch DesktopVisibilityController when needed instead of just once

When creating DesktopTaskbarRunningAppsController the Quickstep Launcher
might not be available, meaning we pass a null
DesktopVisibilityController to DesktopTaskbarRunningAppsController.
With this CL we refetch DesktopVisibilityController whenever needed.

Bug: 338035946
Test: manual, and DesktopTaskbarRunningAppsControllerTest
Flag: ACONFIG com.android.window.flags.Flags.enableDesktopWindowingTaskbarRunningApps DEVELOPMENT
Change-Id: I8b806e2d0addbf8fb5ab6a3d419a4691c445f223