ActivityPub core: fix handling of unlisted statuses by leveraging a similar strategy as for blocks

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -212,11 +212,11 @@ def fetch_activities_for_context(context, opts \\ %{}) do
     Repo.all(query)
   end
 
-  # TODO: Make this work properly with unlisted.
   def fetch_public_activities(opts \\ %{}) do
     q = fetch_activities_query(["https://www.w3.org/ns/activitystreams#Public"], opts)
 
     q
+    |> restrict_unlisted()
     |> Repo.all()
     |> Enum.reverse()
   end
@@ -321,6 +321,13 @@ defp restrict_blocked(query, %{"blocking_user" => %User{info: info}}) do
 
   defp restrict_blocked(query, _), do: query
 
+  defp restrict_unlisted(query) do
+    from(
+      activity in query,
+      where: fragment("not (?->'cc' \\?| ?)", activity.data, ^["https://www.w3.org/ns/activitystreams#Public"])
+    )
+  end
+
   def fetch_activities_query(recipients, opts \\ %{}) do
     base_query =
       from(