bookmarks: write bookmarks file deterministically
Bookmarks are internally stored as an unsorted dictionary. Let's at
least write out the bookmarks file in a deterministic order so it is
easier to test, diff, etc.
Differential Revision: https://phab.mercurial-scm.org/D2469
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}