revlog: introduce a `display_id` property We currently using the "index file" to identify a revlog in error output. Since we are about to make the "index file" location more volatile, we need something better. We move to use the "radix", as it is close to what we currently use. We could probably do better, as pointed out in the comment, however that would be a quite detour from my current goal. Differential Revision: https://phab.mercurial-scm.org/D10579

revlog: also use radix when computing nodemap data file We have a radix, lets use it! Differential Revision: https://phab.mercurial-scm.org/D10578

revlog: stop usage of `_indexfile` to computing nodemap path We now have the radix explicitely lets use the radix explicitely Differential Revision: https://phab.mercurial-scm.org/D10577

revlog: use a "radix" to address revlog Instead of pointing to the index directly and to derive the other file from that, we directly provide the radix and let the revlog determine the associated file path internally. This is more robust and will give us more flexibility for picking this file name in the future. Differential Revision: https://phab.mercurial-scm.org/D10576

revlog: rename `datafile` to `datafile` We want to make the actual location of the datafile and location more of an implementation details than what is is currently. In that process, we make the attribute private. Differential Revision: https://phab.mercurial-scm.org/D10575

revlog: rename `indexfile` to `_indexfile` We want to make the actual location of the indexfile and location more of an implementation details than what is is currently. In that process, we make the attribute private. Differential Revision: https://phab.mercurial-scm.org/D10574