QML SVG, PDF & QQuickImageProvider rendering ignores Screen.devicePixelRatio

QML Images always render SVG, PDF and QQuickImageProvider with a device-pixel-ratio of 1.0, regardless of the actual screen dpi unless sourceSize is set.

This is always pixellated on Hi-DPI screens:

import QtQuick 2.15

Image {
  source: "icon_extensions.svg"
}

This is causing serious difficulty in making QML-based applications support hi-dpi and mixed-dpi platforms, such as Windows 10/11, as sourceSize cannot be set without also explicitly setting the Image height and width.

So far the closest thing I've found to a workaround is to hard-code the device-independent-pixel size of the (eg) SVG into the QML, like so:

import QtQuick 2.15

Image {
  source: "icon_extensions.svg"
  // Manually looked up from the SVG
  sourceSize.width: 24
  sourceSize.height: 24
}

This is not generally acceptable, as it means every single Image item has to be set to an explicit size that must match the SVG it loads.
I have not yet found any QML API that exposes the 'original native' size of an Image source.

This does not appear to be related to QTBUG-94855.

The issue seems to be that qquickimagebase explicitly sets a device pixel ratio of 1.0, unless the sourceSize has been overridden or there is an "@2x" version of a bitmap

    if (loadOptions & HandleDPR) {
        const qreal targetDevicePixelRatio = (window() ? window()->effectiveDevicePixelRatio() : qApp->devicePixelRatio());
        d->devicePixelRatio = 1.0;
        bool updatedDevicePixelRatio = false;
        if (d->sourcesize.isValid())  // BUG!! This check prevents SVG, PDF and QQuickImageProviders from rendering at high quality
            updatedDevicePixelRatio = d->updateDevicePixelRatio(targetDevicePixelRatio);

        if (!updatedDevicePixelRatio) {
            // (possible) local file: loadUrl and d->devicePixelRatio will be modified if
            // an "@2x" file is found.
            resolve2xLocalFile(d->url, targetDevicePixelRatio, &loadUrl, &d->devicePixelRatio);
        }
    }