Animate away Recent Apps section when going to home

Also fix calculation for divider position during this transition
when there are recent apps. Added tests as well.

Flag: com.android.launcher3.enable_recents_in_taskbar
Flag: com.android.window.flags.enable_desktop_windowing_taskbar_running_apps
Test: TaskbarViewControllerTest
Bug: 343522351

Change-Id: Ifffd620c1d4c156b37561584d6e3278b39804439