Add an id "root" by default to the root QML type in the newly created QML file

Currently, when you create a new QML file with "Add New > Qt Quick File," the root QML object doesn't have an id.

I think it's safe to assume that the root level of the QML obejct would have its id as "root" and automatically adding it could save time for the user to manuall y specifiy the id. It may be also better to be just an option for the user if they want to add a root id by default with a checkbox in the dialog for example.