[kcms/krunner] Use more accurate text for the positioning modes
"Free-floating" implies that it can be moved around, which it can't (or at least, it doesn't support this officially even if you can move it around with a Meta+drag).
I would like to land this on the stable branch as the feature was just added for Plasma 5.20. So this will require a string freeze exception. CCing @teams/localization to make that request. :)