createImageBitmap doesn't work with svg files (see bug 1841972), so we need to workaround
this in using an Image.
When printing/saving we must rasterize the image, hence we get the biggest bitmap as image
reference to avoid duplications or poor quality on rendering.
In order to minimize the size the of a saved pdf, we generate only one
image and use a reference in each annotation using it.
When printing, it's slightly different since we have to render each page
independantly but we use the same image within a page.