Create a native image class to work with X11 shared memory

It would be possible to create a QNativeImage class and a QPainter::drawNativeImage() function. Or perhaps just
subclass QImage and use the normal QPainter.drawImage. On most platforms
the QNativeImage would just be the same as a QImage with RGB32, but on
X11 could be a QImage created from a shared memory object allowing X to
see the data without a copy. These are not images mapped into video
memory, but are mapped into X memory on X11.