kwin/switchers/compact: Activate window on single click

The compact switcher shows clearly the icon and title for all the windows, so there is no need for an intermediate "select and disambiguate" state.

In this case delay the activation just enough to have visual feedback of the highlight switching to the clicked item.

I consider this more of a small behavior change than a bugfix, so not proposing it for cherry-pick

BUG: 488722
FIXED-IN: 6.2