Test desktop immersive mode in CI

[jdm]

If we disable the code that checks for user input, it should be possible to do a smoketest that entering and exiting immersive mode on desktop is possible using the glwindow backend. This would hopefully avoid regressions like #26340.

[asajeffrey]

This is probably a good idea, but it wouldn't have caught #26340 since on our CI machine it doesn't crash, it produces a black screen instead. This is most likely issues with driver bugs on different mac GPUs, so I'm not sure how to deal with it in CI.