Put `qmlImportPaths` into some module

Currently to make QtCreator aware of custom QML import paths, we have to define magic property `qmlImportPaths`.

Product { 
    name: "myProduct"
    property stringList qmlImportPaths: [sourceDirectory + "/path/to/qml/"]
}

https://doc.qt.io/qbs/porting-to-qbs.html#qml-import-path

I think it would be much better, if we had dedicated Qbs module for this, so that instead of the above, one could write

Product { 
   name: "myProduct" 
   qtcreator.qmlImportPaths: [sourceDirectory + "/path/to/qml/"] 
   Depends { name: "qtcreator" }

}

This would be much more cleaner and consistent with the Qbs design. It could also pay back if more properties affecting QtCreator are going to be introduced in the future.