Shortcut: Swap focused main window with previously focused window

[ubuntudroid]

Is your feature request related to a problem? Please describe.
I usually have three or more windows open on my laptop. Using the tall layout I often find myself swapping one of the non-main windows with the main one when checking something in those windows only to swap the previous main one back to main a few seconds later (a little bit like opt-tabbing). That becomes a bit tedious when doing very often (swapping the two windows as main windows back and forth).

Describe the solution you'd like
Pressing the shortcut for swap focused window with main window while the main window already is focused could swap it with the previously focused window, but keep the focus on the main pane.

Describe alternatives you've considered
Right now I am using opt-tab + the shortcut for swap focused window with main window. This works, but it's not super convenient. If there is no good way to implement my preferred solution I will likely just set up an own shortcut using Alfred.app or BetterTouchTool which combines those two. However it would be another shortcut to memorise.

[maxandersen]

maybe have the short cut for focused main window when the focus is on the main focused window be to swap back.

so it becomes a toggle - that would be super nice.

[syl20bnr]

This shortcut would be awesome and make the Two Panes layout even more usable.
Returning from main window to last focused window is deeply needed, it is a pain to be forced to cycle through multiple windows just to get back to the previously focused window.

In other terms:
- changing focus to main windows is O(1)
- thus changing back focus to previously focused window should also be O(1)

See issue: #1313

[syl20bnr]

shameless ping @ianyh 👼🏻

[syl20bnr]

mmm will open a new issue about this, this is a different feature request.

[ianyh]

Done in #1390