ActivationManager should use a tagged service iterator

Turns out Drupal 10.x core branches are not using the AutowireIterator attribute anywhere, so in the name of safety, this should probably not be backported.

Assigning to @tim.plunkett for review and commit, as this is the kind of backend clean-up he'll appreciate.

Changed my mind: this should be partially backported. The test should be backported for consistency, but the actual change shouldn't be.

tim.plunkett → made their first commit to this issue’s fork.

Merged to both!