[HEIC] Content-Type: image/heif offers to download the image, rather than showing it as an image document
<rdar://problem/110667964>
Pull request: https://github.com/WebKit/WebKit/pull/14894
Committed 265091@main (1ad9aed19a4b): <https://commits.webkit.org/265091@main> Reviewed commits have been landed. Closing PR #14894 and removing active labels.