Fix focused error of embedded task fragments

If a display has freeform windowing environments such as Desktop
or XR device, then resumed activity of task fragment will be set
to focused app. However, it can break focused state in embedded
task fragments.

Thus, allow it only if a focused task is different from a next task.

Bug: 343252725
Test: Settings(AE) > Launch SubSettings > Check focused app/window
Change-Id: Ib62ecb7c8e0fe453149f51c610c34d97bbde7cb1