R1:e8985fc9e723

Differential - change "closed by commit" comment to real transaction

Summary:
Implements a new transaction - still TYPE_ACTION - but using a new DifferentialAction::ACTION_COMMIT_CLOSE. Augment rendering as necessary to display this new transaction. Saves enough information so T3686 is possible but stops short of implementing a popup to display this information. Fixes T5875. Ref T3686.

One small display oddity - this new transaction now renders at the top of the transaction group whereas when it was a…