All known actions from Slack's Block Kit interactive components, message actions, dialogs, and legacy interactive messages.

TODO: BlockAction's default generic parameter (ElementAction) might be too specific to allow for this type to be used as a constraint on SlackActionMiddlewareArgs' Action generic parameter.

If someone were to instantiate SlackActionMiddlewareArgs<BlockAction>, would it work? We need it to work as long as SomeNewAction implements BasicElementAction.

We don't want to substitute BlockAction with BlockAction here because that means the completions offered when no generic parameter is bound would be limited to BasicElementAction rather than the union of known actions - ElementAction.