R1:e5906f4e127e

In Differential standalone views, disable some keyboard shortcuts which don't work

Summary:
Ref T13164. See PHI693. In Differential, you can {nav View Options > View Standalone} to get a standalone view of a single changeset. You can also arrive here via the big changeset list for revisions affecting a huge number of files.

We currently suggest that all the keyboard shortcuts work, but some do not. In particular, the "Next File" and "Previous File" keyboard shortcuts (and some similar shortcuts) do not…