No multisampling/antialiasing with ANGLE in Windows

Requesting multisampling in a QWindow with surface type QWindow::OpenGLSurface is ignored when the Qt build is based in the ANGLE (non-opengl) renderer.

To reproduce this, use the OpenGL Window example included with Qt and:

1) In file openglwindow.cpp comment-out line 129 and add immediately below:
QSurfaceFormat surfaceFormat = requestedFormat();
surfaceFormat.setSamples( 4 );
m_context->setFormat( surfaceFormat );

This sets the number of samples per pixel to 4 for multisampling.

2) Build and run in the non-opengl (ANGLE) Qt build, you should observe pixelated edges as in the attached image. QSurfaceFormat.setSamples(4) is not working.

3) Build and run in the opengl Qt build, you should observe smooth edges as in the second attached image.