revlog: move censoring code in a dedicated module This code is quite specific and we are about to add more of it for revlog-v2 (and other derived version). So we move this code in a dedicated module in `mercurial/revlogutils/`. This looks like a good fit. The diff is huge because I used `hg copy` to create the new file so that we keep the history of the censor code. Differential Revision: https://phab.mercurial-scm.org/D10789

censor: reduce risk of censor test blowing up output limit The censored file is really big, and we keep using `hg cat` on it, with the assumption that it is censored. However, when it is not censored, the amount of extra line output is huge and quickly saturate the backlog of terminal and CI system. Differential Revision: https://phab.mercurial-scm.org/D10788

revlog: store sidedata in their own file This makes sidedata manipulation simpler and results in more compact data when traversing either data or sidedata. Differential Revision: https://phab.mercurial-scm.org/D10787

revlog: fix docket.date_filepath docstring This was copy-pasted too quickly. Differential Revision: https://phab.mercurial-scm.org/D10786

revlog: use dedicated code for reading sidedata We are about to introduce a new, dedicated, file to store sidedata. Before doing so, we make sidedata reading go through different code as reading data chunk. This will simplify some of the complexity of the next changesets. The reading is very simple right now and will need some improvement later to reuse some of the caching strategy we use for the data file. Differential Revision: https://phab.mercurial-scm.org/D10785

revlog: simplify "partial read" error message We are about to reuse this message in more places and the current handling is pretty hard to read. So we eat two pie with one stone and clean up this. Differential Revision: https://phab.mercurial-scm.org/D10784

revlog: no longer return sidedata from `_revisiondata` All users have been migrated. When they was introduced sidedata where grouped with the actual revision data and unpacking one came with the other. Sidedata moved be stored "independently" and it no longer make sense to retrieve both at the same time unconditionnaly. Differential Revision: https://phab.mercurial-scm.org/D10783

revlog: use `self.sidedata` directly in `revlog.clone` We want to change `revlog._revisiondata` signature, so we need to migrate users away. Differential Revision: https://phab.mercurial-scm.org/D10782

revlog: use `self.sidedata` directly to construct changelogrevision We want to change `revlog._revisiondata` signature, so we need to migrate users away. Differential Revision: https://phab.mercurial-scm.org/D10781

revlog: implement sidedata without using _revisiondata When they was introduced sidedata where grouped with the actual revision data and unpacking one came with the other. Sidedata moved be stored "independently" and it no longer make sense to retrieve both at the same time unconditionnaly. We start with changeset the implementation of the `revlog.sidedata` command to no longer use `self._revisiondata`. More users need to be migrated to direct usage of this `revlog.sidedata` method. This will be done in the coming changesets. Differential Revision: https://phab.mercurial-scm.org/D10780