Drupal 9 readiness for 1.0-alpha2 release

Problem/Motivation

Because Item is not deleted from all language indexes for Multilingual setup. → is postponed and Make language suffix a configuration → Needs work, we need to stay on the 1.0-alpha2 release. But we need 1.0-alpha2 release to be Drupal 9 ready by forking this issue.

Steps to reproduce

See Item is not deleted from all language indexes for Multilingual setup. →
See Make language suffix a configuration →

Proposed resolution

Make the 1.0-alpha2 Drupal 9 ready

Remaining tasks

1. Fork this issue - DONE
2. Modify the 8.x-1.0-alpha2 branch for use in Drupal 9 - DONE
3. Use the forked branch in Drupal 9 instead of the current release branch - DONE

User interface changes

None

API changes

None

Data model changes

None