Update desktop mode flag checks to include device config check

Update `DesktopModeStatus.canEnterDesktopMode()` to include the desktop
windowing flag check. Replace all uses of
`DesktopModeStatus.isEnabled()` with
`DesktopModeStatus.canEnterDesktopMode()` to check both the state of the
flag and whether the device is compatible with desktop mode.

Flag: None
Bug: 339093954
Test: atest WMShellUnitTests:DesktopModeLoggerTransitionObserverTest
Test: atest WMShellUnitTests:DesktopTasksControllerTest
Test: atest WMShellUnitTests:FreeformTaskListenerTests
Test: atest WMShellUnitTests:RecentTasksControllerTest
Test: atest WMShellUnitTests:DesktopModeWindowDecorViewModelTests
Test: atest WMShellUnitTests:DesktopModeWindowDecorationTests

Change-Id: If0846062c2234f1d89fcde271150f3e613fd45cb