Fix KI in test and re-enable for postsubmit.

- The taskbar stashing logic with hardware keyboards was different
  between tests and user experience; aligned the test to be the
  same.
- There is still a previous test failure that only occurred in
  post submit, so also add ScreenRecord to diagnose it
- Once that is resolved, can promote the test to PRESUBMIT.

Test: testQuickSwitchToPreviousAppForTablet
Flag: NA
Fixes: 318544733
Bug: 314873201
Change-Id: Ia813eb0294d759c40d90cec7a8e9a7e0aea2d917