Mention icon for multi-line suggestions

See the full discussion, starting at !110319 (comment 1254864131), for what we could do to improve https://docs.gitlab.com/ee/user/project/merge_requests/reviews/suggestions.html#multi-line-suggestions. I've scored this item as tw-weight5 because I have a strong, strong hunch that I'll need to redo more than just a paragraph. Spidey-sense 🕷 says it will mushroom.

The following discussion from !110319 (merged) should be addressed:

• @marcel.amirault started a discussion: (+7 comments)

  @CBID2 Thanks a lot, I have a few suggestions to fix the pipeline, as well as one to address the changes requested in the issue.

  FYI, if the pipeline failed, you can click on the job with the red ❌ in the pipeline (above), which brings you to the job log. If you scroll down, you should be able to get a hint at the problem. In this case, the job log is: https://gitlab.com/CBID2/gitlab/-/jobs/3669642502

  And we can see on line 37 and 38 that:

  doc/api/project_snippets.md:98 MD046/code-block-style Code block style [Expected: fenced; Actual: indented]
  doc/api/project_snippets.md:129 MD012/no-multiple-blanks Multiple consecutive blank lines [Expected: 1; Actual: 2]

  MD012 is easy enough, we just had two many newlines, we only ever do one at a time, never 2 in a row.

  MD046 is harder, because the tool is just confused with the markdown. But looking at that line I could see that the table row got split in two with an extra newline, so hopefully putting it all on one line again will fix that one too.