<attachment> optional action clickable text, to show action like "Tap to download", and then "Downloading...". <rdar://105250367>
Pull request: https://github.com/WebKit/WebKit/pull/10164
Committed 260393@main (e93a4bd9da8d): <https://commits.webkit.org/260393@main> Reviewed commits have been landed. Closing PR #10164 and removing active labels.