Prevent system ui applications from entering dw

Don't show app handle and make `moveToDesktop` no-op to prevent entry
with keyboard shortcut. If request comes directly from activity via a
launch straight into freeform, force activity to be fullscreen.

Fixes: 340189815
Test: atest WMShellUnitTests:DesktopModeWindowDecorViewModelTests
Test: atest WMShellUnitTests:DesktopTasksControllerTest
Change-Id: Ieade491fac2019b8dbbd29ecc89bdb62aab94bbf