revlog: split constants into a new `revlogutils.constants` module We want to split some logic out of the main revlog file (the delta computing logic). However, this logic needs access to multiple constants related to the revlog. So we move all revlog related constants into a new module that could be imported from multiple places. We don't copy the file (preserving blame history) because there are only a few moving lines. Also, copying the file would result in annoying merge conflicts with ongoing work from others contributors.