Alt+Tab doesn't behave optimally with Window Stacks

[pwall2222]

The current implementation for #135:
Windows in the same stack are always consecutive in the list and not recency-based ordered but stay in a predefined order.

I don't know if this is intended but it is confusing and should be changed, let me explain why:
If you have windows A and B in the same stack, let's say A is always immediately before B in the list, from A pressing Alt+Tab will bring you to B but from B pressing Alt+Tab will keep you on the same window.

This is inconsistent and not practical, Alt+Tab should never keep you on the same window unless it is the only one.

Furthermore, I don't think grouping windows in the same stack is a good idea, it brakes the behavior of this sequence of actions:

1. Alt+Tab
2. Release everything
3. Alt+Tab
   We are used to assume this sequence will bring you back where you started, but currently it is not the case, this is a convention in almost every other environment and also very useful when your workflow alternates between two windows.

In conclusion I suggest to avoid grouping stacked windows at all and order all the windows by recency ignoring stacks, I believe this is how it works currently in Pop!_OS. If you want to move inside the same stack there are the "Focus window left" and "Focus window right" shortcuts already.

Originally posted by @Tommimon in #135 (comment)