availableLocales are not prebuild

in doc mentioned

https://doc.qt.io/qt-5/qml-qtquick-virtualkeyboard-settings-virtualkeyboardsettings.html#availableLocales-prop

This list is read-only and depends on the build-time configuration of the virtual keyboard.

but I tried added this in `basic` demo, it returns an empty list.

Component.onCompleted: {
console.log("uiLanguage ",Qt.uiLanguage)
console.log("availableLocales:", VirtualKeyboardSettings.availableLocales)
}