Qt Design Studio assigns rotations as rotation.x, rotation.y, rotation.z.

The asset importer uses this syntax:
rotation: Qt.vector3d(-90, 0, 0)
scale: Qt.vector3d(0.2, 0.2, 0.2)

We should not mix different ways of defining properties.
For QDS rotation.y is the most natural way to assign such properties,
because Qt.vector3d() is technically a function.

The importer should create files that are 'designer-friendly'.

The current syntax (Qt.vector3d(0.2, 0.2, 0.2) is somewhat supported in QDS. Files do show up,
but it would require extra effort to support this syntax in the property editor.