R1:77b3efafbd4e

Use ModularTransactions for accept/reject/resign in "differential.createcomment"

Summary:
Ref T10967. `differential.createcomment` is a frozen API method which has been obsoleted by `differential.revision.edit`.

It is the only remaining way to apply an "accept", "reject", or "resign" action using the old "ACTION" code.

Instead of using the old code, sneakly apply a new type of transaction in these cases instead.

Then, remove all the remaining old code for this stuff on the write pathways.

Test Plan…