rawdata: introduce a `rawdata` method on revlog This method aims at replacing `revision(..., raw=True)` call. The purpose of data returned without and without raw are different enough that having two different method would make sense. This split is motivated by other work aiming at storing data on the side of the main revision of a revlog. Having a cleaner API makes it simpler to add this work. The series following this first changesets is organised as follow: 1) add `rawdata` method everywhere it is useful 2) update all caller 3) implement all `rawdata` method without using `revision` 4) deprecate the `rawdata` parameter of `revision`