Make focus_visible_window behaviour in stack layout consistent with other layouts

[sahinakkaya]

Problem:

Quoting the documentation:

Visually select and focus window

Display overlay numbers and alphabets on the window, and switch the focus to the window when you press the key. When there are only two windows, the focus will be switched directly without displaying the overlay.

The emphasized part is what this issue is about. It indeed switches to other window when there are only two windows, except when the layout is stack.

Describe the solution you'd like
I expect the behaviour in stack layout to be consistent with other layouts. When there are two windows in the stack, focus_visible_window should focus other window without displaying window selection overlay.

Describe alternatives you've considered
At least it should be optional if backwards compatibility is an issue.