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

This is like QTBUG-42606, but for non-integer scale factors. It is reproducible in KDE Plasma by setting QT_DEVICE_PIXEL_RATIO via a systemwide scale factor (System Settings > Display & Monitor > Displays > Scale) and then viewing a piece of QML text that has `RenderType: Text.NativeRendering` set.

See the attachments, which are from QTBUG-42606. The same issue is visible, but for non-integer scale factors. With a scale factor or 1 or 2, all three lines of text look fine. With a non-integer scale factor, the middle puece of text looks blurry.

Switching to Text.QtRendering resolves the issue completely.