Fix alt tab icon size on hidpi screens

Commit message of last commit:

When calculating the icon sizes for the alt tab switcher we have to use the scaling factor not only when checking whether the icons will fit on the screen, but also when actually setting the size of the icon, just as we do with the window switcher icons.

Since we already map the baseIconSizes array to include the scale factor, simply always using those values fixes the issue.

Fixes #1325 (closed)