When unpublishing or deleting a page or snippet, it would be useful to have a summary of what other objects uses the page/snippet, so that users know what the implications are.

The snippet delete confirmation page currently shows the number of other objects that use the snippet. Now that we have the powerful reference index, we should be able to show all the usages efficiently.

Meanwhile, for other views (page delete confirmation and page/snippets unpublish confirmation), we do not show any usage information at all.

For the record, we currently don't have a Usage view for pages (see #1722). The existing "usage" view for pages shows you the usage of the page types, not the page instances themselves. Before adding this usage summary to the delete/unpublish views, I think ideally we should have the Usage view itself first.

Work required:

• Extract the usage view for snippets, images, and docs into a generic view and make the other views extend from it.
  • Extract generic UsageView and use it for snippets, images, and documents usage views #10007
• Implement a page usage view based on the generic usage view.
  • Provide usage figures for pages too #1722
• Add the usage summary on the delete and unpublish confirmation views on pages and snippets.
  • Show on delete information in usage views to be linked from delete/unpublish confirmation views #10072