MastoAPI: Also return text_url in attachments.

lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -73,6 +73,7 @@ def render("attachment.json", %{attachment: attachment}) do
       url: href,
       remote_url: href,
       preview_url: href,
+      text_url: href,
       type: type
     }
   end

test/web/mastodon_api/status_view_test.exs

@@ -71,7 +71,8 @@ test "attachments" do
       type: "image",
       url: "someurl",
       remote_url: "someurl",
-      preview_url: "someurl"
+      preview_url: "someurl",
+      text_url: "someurl"
     }
 
     assert expected == StatusView.render("attachment.json", %{attachment: object})