Text.NativeRendering on Linux/Freetype produces pixelated and offset labels with non-integer QT_DEVICE_PIXEL_RATIO

This is a continuation of QTBUG-67007. We tried to fix it but accidentally made it worse, and this bug tracks the current state.

In a nutshell, when QT_DEVICE_PIXEL_RATIO is set to a non-integer value (e.g. 1.5), text rendered with Text.NativeRendering is not rendered correctly. Originally the problem was that it was pixellated. In QTBUG-67007, we tried to fix that, but accidentally made it worse: now it is not only pixellated, but also visually offset from its desired location. See the attached image.

Workaround: set Text.QtRendering for every QML item that produces text. However for a large codebase this can be quite troublesome, and obviously an upstream fix is preferred.