Should be able to mark comments as spam from front end

As requested in [#meta4217](https://meta.trac.wordpress.org/ticket/4217)

> After the block editor was introduced, one can't anymore jump over to the editing panel for a post in order to mark a comment as spam. Instead you have to browse through page after page of approved comments, until you reach the relevant date to flag the comment as spam.
>
> If possible, please add (for users with appropriate caps) a possibility to mark a comment as spam directly in the front-end.

The issue names no files, tests, or entry points. Start by locating the front-end comment display and its existing moderation controls, then trace how user capabilities are checked. Done means users with the appropriate capabilities can mark a comment as spam directly from the front end.

Written by the indexing model from the issue text.