R1:7bebfa289aa1

Diffusion commits: add some edge phrases about Revisions

Summary:
This change implements some messages that were only present
from this class:

DifferentialRevisionHasCommitEdgeType.php

But not in its inverse class:

DiffusionCommitHasRevisionEdgeType.php

In short:

| Before | After |
|-----------|-----------|
| {F313282} | {F313281} |

Closes T15314

Test Plan:
Visit a Diffusion commit and use the sidebar menu "Edit Related Objects" to:

- add 1 revision
- add 2 revisions
- remove 1…