rank: naive rank property computation and retrieval
This stores the rank (size of the ancestor set of a revision, including itself)
in a changelog field and allows this property to be retrieved.
This new property is used as part of stable-range computations, which will be
introduced later on.
The value is computed in a naive way from the definition of the rank. This will
be replaced by a more efficient version subsequently.
Differential Revision: https://phab.mercurial-scm.org/D12139
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}