Track ghostly inlines across file moves

Summary:
Ref T7447. Ref T7870.

• Forward: When rendering some file "B" which was moved from "A", port ghosts for both "A" and "B" to it.
• Backward: When porting a comment on "X" which was moved from some "Y", allow it to port to a file named "Y" if it can't find a file named "X".

Test Plan:
Before:

{F377809}

After:

{F377806}

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7447, T7870

Differential Revision: https://secure.phabricator.com/D12493