Show link to megamenu dropdown content in site editor

Currently, the association between the "HM Megamenu Block" and its contents is a bit hard to navigate:

You can choose the menu template to associate with the dropdown trigger link in the block settings sidebar, but the "Site Editor" link just goes to a landing page. It would be better if there were a direct link to edit the pattern used for the dropdown contents. A stretch goal beyond that could be to show the dropdown contents directly in the editor, or at least a preview of it.

Start in the HM Megamenu Block settings sidebar and trace the existing Site Editor link and menu-template association. Done means the link opens the pattern used for the dropdown contents directly; showing the contents or a preview is an optional stretch goal.

Written by the indexing model from the issue text.