kcms/users: don't let "Choose File…" text overflow
When using a language that's wordier than English and this label becomes a two-line string, currently the layout breaks and the string overflows because the Label item that draws it has no maximum height and elision mode set.
This commit fixes that by setting them accordingly, and also using a standard icon size for the icon so that there's actually enough room for two lines of text.
BUG: 458614 FIXED-IN: 5.24.7 (cherry picked from commit 0dad5f07)