Allow nested condition groups for more complex conditions

Needs reroll, sorry.

This should be applied against the 2.0.x branch, just had our first (Drupal 10 compatible) release there, will commit this to there so it is available on dev branch immediately.

This patch works great for me and immediately solved my problem. Rerolled for 2.0.x-dev
(Seems there is no "test with" option for 2.0.x-dev) for automated testing.

Rerolled.

This hopefully fixes the tests.

This needs test coverage.

Tested #16 and it fails to patch. block_visibility_groups_admin/src/Tests/GroupListerTest.php is the wrong location and case. Location should be block_visibility_groups_admin/tests/Functional/GroupListerTest.php

I haven't had time to work on writing tests but I did re roll 16 to make it work again.