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:

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 revision
• remove 2 revisions
• add 1 revision, remove 1 revision
• add 2 revisions, remove 2 revisions

Check that you don't see phrases like "added an edge" anymore.

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: speck, tobiaswiese, Matthew, Cigaryno

Maniphest Tasks: T15314

Differential Revision: https://we.phorge.it/D25306