Calling QFont::setStretch has no effect when the DirectWrite font engine is in use.

To reproduce:
1. Build and run the attached test app.
2. Click on the 'stretched' checkbox and observe that the text stretched correctly using the GDI font engine.
3. Click on 'DirectWrite'. Notice that the stretch is no longer present.

From looking at the DirectWrite API documentation, arbitrary font scaling doesn't seem to be supported, so perhaps Qt should just fall back to the old GDI font engine if a stretch is specified.