Backlinks aren't added for wiki pages referenced in a diagram content starting with XWiki 14.8

[Farcasut]

Starting with XWiki 14.8, the platform backlinks functionality was deprecated , see https://jira.xwiki.org/browse/XWIKI-16192 . Right now, the diagram application still uses the deprecated way to add backlinks when a wiki page is referenced inside a diagram content. Because of this, now when a referenced page will be renamed / moved, the diagram content won't be updated to have the new link.

Note that this is a 'sub-issue' of #245 , along with #295. This and #295 have separated causes, but both break the update links functionality.

Note that after this issue is fixed, there would still be problems with updating links on Diagram application versions >= 1.20.3 because of #295 (if it isn't fixed)