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Patch Qt to make QQuickWindow renderer to use real size

Alvin Wong requested to merge alvinwong/krita:alvin/qt-qquickwindow-size-patch into master

This patch is necessary to make QQuickWindow set up the renderer's projection matrix in a way that would allow pixel-perfect rendering from QtQuick2 when the high-DPI scaling (devicePixelRatio) is non-integer.

I found this when experimenting with !1329. Without this patch, there is just no way to reliably size items in a way that can let us render the canvas item correctly in fractional scaling (only for the QtQuick2 port; the normal OpenGL canvas does not need this).

I've tested this patch in the Ubuntu 18.04 appimage docker and I believe it does what I expect. I don't think there should be any harm to have this patch applied for the 5.0.4 release (it wouldn't cause any visible changes, at most it would make the Touch Docker look very slightly different), but if there are any concerns it can wait after 5.0.4.

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