Reports show things from config/optional as "new" even though they come from modules

Investigation:

It looks like the reports are now showing things from config/optional as "new items added". For instance, if you run the report for type Search pages, it shows the Node and User search pages in the "Added configuration items" section. These come from core/modules/node/config/optional and core/modules/user/config/optional.

This seems to be the root cause of all of the problems.

I got this figured out, with tests. There's a new section to the report page (and a new Drush command) that shows the optional items that are not currently in active config, and the Added report now excludes things from config/optional.

If you update to this commit, you'll need to do a container rebuild, because there are new services and changed constructors on classes.