The previous method of relying on the order of windows returned by appium to determine window z-order proved not to be reliable. Instead use p/invoke to read `NSWindow.orderedIndex` on a timer and display it in a text box in the `ShowWindowtest` window.

This commit doesn't update the tests to use this new info though.

And update the tests to use the value of `NSWindow.orderedIndex` exposed in 0cc0443 instead of relying on appium to give us a z-ordered list of windows.

When a window is closed, its parent window is set to null, which caused this code to run. This line caused the parent window to be brought to front, and should have also caused any other child windows to be brought to front, but it seems OSX ignored those requests, causing #8878.

Simply don't bring the parent window to the front when a child window is closed. I couldn't work out why this code was necessary anyway, and all integration tests still pass.

Fixes #8878.