Comments: bulk actions undo

I think if we have a persisted item selected for bulk, we should offer the undoable action in the bulk action list.

For example:
- Navigate to pending
- Select all comments
- Approve
- Try to unapprove again in this view. We end up needing to exit bulk edit mode and expanding the comment to act on it.

Start by reproducing the pending-comments workflow: select comments, approve them, and inspect the bulk action list without leaving bulk edit mode. Trace the comments bulk-action UI and make the undoable opposite action available for persisted selected comments. Done means the action can be performed from the same bulk view; verify the workflow in the relevant UI tests if present.

Written by the indexing model from the issue text.