Add close_button option to test_viewports

[pm100]

This make the test excercise the window recreation logic, that resulted in several bugs - see #4862

Adds a check box that turns the close button on and off for child windows

[emilk]

Thanks!

[pm100]

@emilk - this allows full testing of the issues associated with #4862. You can see the different behaviors with mac, linux, windows and with wgpu or glow. I believe my PR fixes them all (I have now tested on linux)

PS, can you please look at discussion #4871, I am stuck