Exclude embedded TaskFragment from non-app windows

Before, when a TaskFragment is included in the transition, it is treated
as non-app window, which caused flicker when open/close Task with
embedded TF.

Bug: 207070762
Test: atest SystemUITests:RemoteTransitionTest
Change-Id: Iaf26b70e33f82d86988cde0a7eea10acc4e0d6bb