ScalableImageDecoder is only tried when USE(AVIF) is enabled
<rdar://problem/106184839>
Pull request: https://github.com/WebKit/WebKit/pull/10989
Committed 261161@main (fe519f43f2e5): <https://commits.webkit.org/261161@main> Reviewed commits have been landed. Closing PR #10989 and removing active labels.