upgrade: use rawsize() instead of revlog index The revlog index is a very low-level data structure and it shouldn't be exposed to the storage interface - at least not in its current form. upgrade.py is the only consumer of the index attribute on file storage in the repository. This commit rewrites that final consumer to use rawsize() instead of going through the index. This is actually the more proper API to use, as rawsize() will accurately report the size of revisions which have a negative size in the index. Differential Revision: https://phab.mercurial-scm.org/D4719