Keyboard shortcuts to cycle through stacked windows

[harshpatel333]

When several windows are snapped to the same area, such as three windows on the left half, only the front one is visible. The stacked window list on hover lets you reach the covered windows with the mouse, but there's no way to do it from the keyboard.

I'd like to add two assignable actions, Cycle Stacked Windows and Cycle Stacked Windows Backward. Each press brings forward one window from the stack the focused window belongs to. I've implemented this in #1883. I'm happy to change the naming, where it lives in Settings, or how it behaves.