When instantiating an action, the placements configured on the class

were used directly, with state stored on them. That failed when

subclassing an action or when reusing an action across tests.
Placements are now cloned when instantiating the action, avoiding this

scenario. It's now safe to have multiple actions share a placement or

list of placements for their definitions.

Unit tests pass.
Verified this fixed unit test issues with in-progress changes.