[lookandfeel] Allow OSD on a lockscreen use its preferred size

It still look far too alien comparing to a native PlasmaDialog style due
to the positioning, fractional scaling sizing issues and background
differences. This commit brings them somehow closer to each other.

lookandfeel/org.kde.breeze/contents/osd/OsdItem.qml

@@ -34,6 +34,8 @@ RowLayout {
     Layout.minimumHeight: Layout.preferredHeight
     Layout.maximumWidth: Layout.preferredWidth
     Layout.maximumHeight: Layout.preferredHeight
+    width: Layout.preferredWidth
+    height: Layout.preferredHeight
 
     PlasmaCore.IconItem {
         Layout.leftMargin: PlasmaCore.Units.smallSpacing