revlog: use a `reading` context in `_enforceinlinesize` We are about to enforce reading context on various operation, so we make sure top level method are in the right context. In the future we might move the responsibility of opening the revlog for reading higher in the call chain but lets limit the disruption for now.

revlog: drop the df argument to `sidedata` The intend of this argument is better filled by the `revlog.reading` or `revlog._writing` context. So we drop it to leave rooms for further cleanup and improvements.

revlog: drop the df argument to `rawdata` The intend of this argument is better filled by the `revlog.reading` or `revlog._writing` context. So we drop it to leave rooms for further cleanup and improvements.