R1:bdda7eed0734

Improve display behavior for write locks held by omnipotent users

Summary:
Ref T13614. When an omnipotent user calls "synchronizeWorkingCopyBeforeWrite()", we record a WorkingCopyVersion record with a null "userPHID". The UI then renders this as "Unknown Object (????)".

Improve this behavior:

- When no PHID is available, just render nothing in the UI (this doesn't seem meaningfully different from no version existing at all).
- Allow callers to provide an acting user PHID, similar to Editor.

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