Reinstate drupal_common_theme() and deprecate it

We'll need to update https://www.drupal.org/node/3488470 →

Should have done it in the first place. Looks great.

Committed/pushed to 11.x, without the test coverage since we don't require test for pure bc-wrappers.

catch → closed merge request !10364

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

AFAIKT, the change record is correct.