The image provider can already render SVG images supplied
as format_data due to using QImage as backend.
This unfortunately only works correctly as long as the SVG image is
not scaled, as the image provider ignores the requested_size parameter
for format_data, causing the SVG image to be first rendered at its default size
and then scaled at the bitmap level, resulting in a very blurry image.

As there does not appear to be any easy fix for this when working with
the format_data type add a new data type called format_svg_data that
properly renders the SVG image at requested size with QtSvgRenderer.

Also the documentation has been updated to include format_svg_data
and an example has been added.