Drupal 10 readiness

This patch should fix the issues spotted via the upgrade status module. But as the core/jquery.once asset library is deprecated in Drupal 9.3.0 and its replacement was added in Drupal 9.2.0 it means the module can't support D8 and D10 in the same release, so this patch drops the D8 support.

The patch had been failing on a recent upgrade in the info.yml file. Attached is a new version of the patch.

Noting that I could not get the patch from #3 to apply, but the patch from #2 worked with and without the patch linked in #2.

I'm using the latest release 2.0.0-beta1 (30 April 2020), perhaps #3 applies to the module in conjunction with a patch from yet another issue.

Automatically closed - issue fixed for 2 weeks with no activity.

This ticket is marked fixed, but I'm not seeing any reference to it in a new release.