Add back 'disabled' redirects

I've started work in the MR on this.

Things remaining:

• Have an upgrade path that doesn't assume that the redirect entities are in the database.
• Get tests passing (I've not touched them, I assume that they will break with these changes.)
• Add some more tests for enabled/disabled redirects.
• If the status column was in Drupal 6 redirect, add the migration code for that.
• See if the submodules need any changes.
• Consider changing the signature of \Drupal\redirect\RedirectRepository::findMatchingRedirect to accept an ENUM so that one could query for only disable redirects.

Uploading a patch to get the tests tested. I've not added any new tests for this functionality yet.

I started working on this feature as well from a different angle (Workspaces support) but didn't consider searching through the issue queue first.

However, after finding this issue, turns out my approach was almost identical, so I incorporated my changes into the existing work here :)

Decided to drop the behavior change for disabling redirects instead of deleting them on path alias updates, I think that should be discussed in a separate issue. This is fully ready for review now :)

reviewed.

Thanks for reviewing :)

berdir → credited alexpott → .

Yeah, maintaining update tests is a pain, not really motivated to do that. Merged.