rhg: Rename some revlog-related types and methods Use "data chunck" and "data" for a revlog entry?s data before and after resolving deltas (if any), repsectively. The former `FilelogEntry` actually only contains data, rename it to `FilelogRevisionData` accordingly. This leaves room to later have a `FilelogEntry` type that wraps `RevlogEntry`. Differential Revision: https://phab.mercurial-scm.org/D11959