Support content edit form on alert banner with Gin

[andybroomfield]

Looks like we need to implement a Gin hook to specify our routes.

/**
 * Register routes to apply Gin’s content edit form layout.
 *
 * Leverage this hook to achieve a consistent user interface layout on
 * administrative edit forms, similar to the node edit forms. Any module
 * providing a custom entity type or form mode may wish to implement this
 * hook for their form routes. Please note that not every content entity
 * form route should enable the Gin edit form layout, for example the
 * delete entity form does not need it.
 *
 * @return array
 *   An array of route names.
 *
 * @see GinContentFormHelper->isContentForm()
 * @see hook_gin_content_form_routes_alter()
 */
function hook_gin_content_form_routes() {
  return [
    // Layout a custom node form.
    'entity.node.my_custom_form',

    // Layout a custom entity type edit form.
    'entity.my_type.edit_form',
  ];
}