WPF apps don't play nicely with the auto-hide taskbar setting

[austinkinross]

Copied from internal OS bug #35513385. Requires Windows 10.

Repro steps:

1. Right-click on your Windows 10 taskbar, go to Taskbar Settings and turn on "Automatically hide the taskbar in desktop mode".
2. In VS, create a new WPF app (for example, File->New->Project (WPF App (.NET Framework) (C#)) in VS).
3. Launch your new app and maximize it.
4. Run your cursor to the side of the screen where the taskbar is hidden.

Expected result: the taskbar becomes visible (like it does if you maximize other apps, e.g. Microsoft Edge)
Actual result: the taskbar remains hidden.

This repros with .NET 6.0 preview 7, and .NET framework 4.5