It now supports copying Markdown, SVG and Images (not in Firefox currently because of lacking [`ClipboardItem`](https://developer.mozilla.org/en-US/docs/Web/API/ClipboardItem) support, but can be enabled in `about:config` and works). It will fetch the data if in a rendered view or when it's an image. Followup to https://github.com/go-gitea/gitea/pull/21629.
