rust-index: variant of assert_py_eq with normalizer expression
The example given in doc-comment is the main use case: some methods
may require ordering insensitive comparison. This is about to be
used for `reachableroots2`
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}