We shouldn't add a data-snippet in the declaration of a snippet,
as they are meant to be drag & dropped, the editor/right panel is going
to add that for you. We generally add them when we copy paste a snippet
definition into another view directly in our sources (ie: template)
Ref: https://github.com/odoo/odoo/pull/87059#discussion_r866903584
Part-of: odoo/odoo#95940
The shape feature only applies to attachments. This moves images from
mass_mailing snippets into attachments so they can be shaped in the
editor.
task-2760157
Part-of: odoo/odoo#84926