Policies should have an `applicable_action_types` callback

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### Is your feature request related to a problem? Please describe.

A lot of policies don't make sense to run on create actions, because they test against the original record. eg. `relates_to_actor_via`. At the moment this will either raise a runtime error, or silently fail.

### Describe the solution you'd like

If each built-in policy could define which action types it worked on, we could emit a compile-time warning if people write policies that don't make a lot of sense or will never pass on a create action.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

No files or tests are named in the issue. Start by locating the built-in policy definitions and the code that validates policies or emits compile-time warnings; determine how action types are represented. Done means built-in policies can declare applicable action types and policies that do not make sense for create actions produce an appropriate compile-time warning.

Written by the indexing model from the issue text.