SDDM theme: stop eliding people's names so aggressively
When more than one user is shown on the login screen, username labels are limited to the width of the avatar so they don't overlap one another. However they are not allowed to become multi-line strings, so they can get elided if they are not somewhat short. This was worsened recently by a change in Plasma 5.24 to increase the size of the username labels, which shortened the amount of text that can be seen without eliding. This commit fixes that problem by allowing constrained username labels to become multi-line strings with up to 3 lines, and adjusting the surrounding layout to visually accommodate this. BUG: 450673 FIXED-IN: 5.24.3