* Make it work for all pages, including those created from content adapters and not backed by a file.
* Allow the `slug` to win, so the new tokens are:
`:contentbasename`:
1. ContentBaseName
`:slugorcontentbasename`:
1. Slug
2. ContentBaseName
Note that a page will always have a `ContentBaseName`, so no need to fall back to e.g. the title.
Closes#11722