Let image diff comments join a batch review

Stanislav Lashmanovrequested to merge
slashmanov/rapid-diffs-image-draft-notes into master

What

On legacy diffs an image comment can be started as a review, the same as any other diff comment, so it joins the batch a reviewer submits at the end. In Rapid Diffs the image comment form only offered "Comment", so image feedback could not be part of a review. This adds a draft action for image positions and wires it the way the file, line and reply forms already do.

Closes #628510 and re-enables spec/features/merge_request/user_reviews_image_spec.rb's "leaves review" example.

Reproduction

  1. Enable the rapid_diffs_default_on_mr_show feature flag.
  2. Open a merge request whose Changes tab contains an image diff.
  3. Click the image to start a comment. It now offers "Start a review" alongside "Add comment now".
  4. Start a review. The comment appears as a draft and is included when the review is submitted.

Merge request reports