R1:3c1f393c812f

When a Paste has a useful alternative rendering in Files, provide a hint

Summary: Ref T13528. When a file in Paste (like a Jupyter notebook) has a good/useful document engine, provide a link to Files.

Test Plan: {F7409881}

Maniphest Tasks: T13528

Differential Revision: https://secure.phabricator.com/D21196