Add test case where enableDisplayWindowingModeSwitching is disabled

This CL adds the unit test for the case where
enableDisplayWindowingModeSwitching is disabled.
No transition should be triggered when the flag is off.

Flag: EXEMPT - add test
Bug: 398115509
Test: DesktopDisplayModeControllerTest
Change-Id: Ibebac692f5bce2e84dbcc4f12f454185cef22f2e