Add new stable Version with full Drupal 9 support

The lack of that release is somehow blocking my tablefield integration tests to pass on D9.
See #3162105: Support translation of Tablefield module and #3157542: Error when having a composer.json dependency on a non-ready D9 module.
I thought that would use -dev, but looks like a valid release is still needed for drupalCI+composer+bare repos.

What would need to be done for tagging a release?

Per https://www.drupal.org/pift-ci-job/1778011 this is not compatible, tests need to be updated at least. Creating a child issue.

#3162786: Add basic testing of using a tablefield value contains tests for creating a field, adding it to an article and creating a node with a table and visiting it. So I'm marking this as Needs review.

I also suggest turning on D9 testing for this project! Minimum versions are PHP 7.3, MySQL 5.7, and D9.0 and/or D9.1

I would love to see a new tagged release as well. There is nothing otherwise preventing this module from being fully Drupal 9 compatible.

Would also love to see a new release tagged.

I tagged a new release 8.x-2.2. Thanks for the reminder!