kcms/landingpage: Use global themes' real names in quick chooser
By using generic "Light" and "Dark" terminology here, we're giving people the mistaken impression that the global theme buttons on the Quick Settings page comprise a generic light/dark toggle switch. But they do not; they are simply quick links to the Breeze Light and Breeze Dark global themes. So let's clarify that by using the actual names of whatever global themes are configured to appear here. BUG: 459367 FIXED-IN: 5.26