Allow Action Definitions to be called as functions.

[crazytoucan]

This PR improves ergonomics for Definition.create():

const SetVisible = TypedAction.create("app::set_visible")<{
  item: string;
}>();

// old way
dispatch(SetVisible.create({ item: "hello-redoodle" }));

// new way
dispatch(SetVisible({ item: "hello-redoodle" }));