revlog: drop the df argument to `revision` 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.

interfaces: drop the `raw` parameters on ifiledata interface In practice it was not implemented since forever. The `rawdata` method fit that purpose. The interface checking does not detect that because it seems to confuse the `_df` argument for the `raw` one. Dropping that `_df` argument in a descendant changesets revealed the issue.

delta-computer: stop explicitly taking file handle The revlog has all the logic for opening and caching such handles, so no need to duplicate it here. In addition, this let the revlog handle that logic by itself which is better.

censors: simply use `revlog.reading` to keep things open dring rewrite We have a dedicated context now, we can simply use it. In practice, we cannot "simply" use it, as `finddeltainfo` still requires the file pointer to be passed explicitly. We will keep the old context manager open for a small bit until we get rid of it in a future changeset.

stream-clone: use `revlog.reading` in `revlog.get_streams` We can get the same result while using more standard method, so we do.

debug-revlog: keep the revlog open for the analysis duration This is more explicit. No performance differences were observed.

repo-upgrade: keep the revlog open while cloning This is more explicit. No performance differences were observed.

verify: keep the revlog open for reading while verifying it This is more explicit. No performances difference were observed.

convert: use `changelogrevision` to fetch changeset data instead of read This `changelogrevision` is a higher level function that will remain simple to use as we refactor the revlog.

revlog: adapt the `reading` check for `unionrepo` We cannot just rely on the length check for the `unionrepo` as the local revlog might be empty while the other revlog contains data. In addition, we need to also open the second revlog for reading when needed.