Make QQuickTextNode public to enable the creation of non-rectangular text areas.

The QQuickTextNode class has a addTextLayout which takes a QTextLayout and presumably sets up the scene to draw it. Can we clean up this class to make it publicly accessible so that users can create their own text items that are not rectangular?

The QTextLayout does all the work of laying it out in a non-rectangular fashion... hopefully the QQuickTextNode just draws it.

This would allow us to create non-rectangular text to use in any way we see fit (for example, creating our own text editor which has mini-games inline with text).