.qml files cannot start with a lowercase

I am not sure if this is strict requirement, but it seems that whenever a `.qml` file starts with a lowercase letter, it is ignored, e.g. it is not present in the `qmldir` and it is not picked up when calling `QQmlApplicationEngine::loadFromModule` (`Module * contains no type named *`).

If this is a strict requirement, than CMake should enforce this format when calling `qt_target_qml_sources`. Otherwise we should look at unlocking that possibility. One issue could be on systems like MacOS where case-sensitivity of files is not a requirement, but that should only affect the finding of files, and not what values are passed and evaluated to `qt_target_qml_sources` itself.