Allow the "Close window" keyboard shortcut to also confirm closing the window when there are multiple tabs open

### Description of the new feature

This, of course, only applies if the "Warn when closing more than one tab" setting is active.
It would make pressing the "Close window" keyboard shortcut behave like clicking the window close button already does: click once to close window, if there's a confirmation dialog because there are multiple tabs opened, click again to confirm. It would be faster and more ergonomical than having to reach for "Enter", especially if the other hand is on the mouse.

### Proposed technical implementation details

_No response_

Start by tracing the "Close window" keyboard shortcut and comparing it with the existing window close-button behavior. Check how the "Warn when closing more than one tab" setting triggers confirmation. Done means invoking the shortcut again confirms the close when the dialog is shown, matching the close-button flow.

Written by the indexing model from the issue text.