Make minimized windows moving to end of focus chain optional

Some users apparently liked the old behavior of moving minimized windows windows to the end of the focus chain. This merge request brings back that behavior but gates it behind a hidden config option. We can add a UI for it later if needed.

To test, add MoveMinimizedWindowsToEndOfTabBoxFocusChain=true to the [TabBox] group of your kwinrc file and restart KWin, then minimize a window and hit Alt+Tab. You'll see that the minimized window has moved to the end the of the Task Switcher's focus chain.

I don't feel particularly strongly about this, but I don't like to hear complaining users, so I thought I'd submit this anyway and see what people think.

BUG: 427840 FIXED-IN: 5.21