In "arc branch" output, sort branches updated in the same second by name
Ref T13546. The new "arc land" workflow can rebase several branches per second. With branches like "feature1", "feature2", etc., this leads to out-of-order listing in "arc branch".
When two branches would otherwise sort to the same position, sort them by name.
Test Plan: Ran "arc branch" after a cascading rebase by "arc land", saw "land5", "land7", "land8", etc., instead of an arbitrary order.
Maniphest Tasks: T13546
Differential Revision: https://secure.phabricator.com/D21316