Add a virtual method to query frame durations without decoding pixel
data. This is needed by the ImageDecoder service to extract timing
metadata upfront for streaming animation decode.
Implement the method for GIF, PNG, WebP, AVIF, and JPEGXL decoders.
For WebP, extract durations from the demuxer during header decode so
they are available before any frames are decoded.
Gfx::Bitmap only supports a bit depth of 8, therefore we refused to
load AVIF images which didn't have this bit depth.
However, we can tell the libavif decoder to reduce the output depth by
setting avifRGBImage.depth to 8. This allows us to support any input
depth.
Makes images load on https://www.ikea.com/ which uses Cloudflare Images
to re-encode their images to 16-bit AVIF.
