Show captions on tablets even when display windowing mode is fullscreen.

Changes the criteria for showing caption on fullscreen tasks to check
if the device is a tablet based on screen size rather than using display
windowing mode.

Bug: 243671025
Test: Manual testing; launched fullscreen tasks on multiple devices with
and without desktop mode flag enabled.

Change-Id: I4550f040daef9c55edaaf42bcfc2004a23e6924f