[lookandfeel] Fix undefined config.fontSize warnings
in lookandfeel/contents/components, config.fontSize is used a few times. This property is resolved correctly when the components are loaded by sddm since theme.conf.cmake contains a fontSize property. However, when these components are loaded by lookandfeel/contents/lockscreen, the log is spammed with warnings about config.fontSize being undefined. By adding a fontSize property to the lockscreen config, these warnings should disappear.