object: add helper functions to handle various forms of a given object and return a normalized one

lib/pleroma/object.ex

@@ -27,6 +27,10 @@ def get_by_ap_id(ap_id) do
     Repo.one(from(object in Object, where: fragment("(?)->>'id' = ?", object.data, ^ap_id)))
   end
 
+  def normalize(obj) when is_map(obj), do: Object.get_by_ap_id(obj["id"])
+  def normalize(ap_id) when is_binary(ap_id), do: Object.get_by_ap_id(ap_id)
+  def normalize(_), do: nil
+
   def get_cached_by_ap_id(ap_id) do
     if Mix.env() == :test do
       get_by_ap_id(ap_id)