DO NOT MERGE: Allow any suitable stack for TestActivity

With change ag/3595036, the stack for the TestActivity is no longer
guaranteed to be FULLSCREEN_WORKSPACE_STACK_ID. Instead, check that it
goes on a suitable fullscreen-type stack, and that the same display
contains the Assistant stack.

Bug: 69859187
Test: Passes on VR Device and Phone

Change-Id: I7b721ca1e35a435181fef5f26e3d8654691ea35f
3 files changed