Adds just a fullscreen window state to kmahjongg. For now the feature won't be saved over session. This will be implemented in future versions.
use KStandardAction::fullScreen ? https://api.kde.org/frameworks/kconfigwidgets/html/namespaceKStandardAction.html#a0e30d17570d5b886e97b1f2cf34ef900
that way you don't have to set the text (which is wrong) nor the icon yourself