cmd/go: synchronize and remove packages duplicated in x/mod #34801
Description
There are several module-related packages that appear in both cmd/go and golang.org/x/mod. They are:
cmd/go/internal/module => golang.org/x/mod/module
cmd/go/internal/semver => golang.org/x/mod/semver
cmd/go/internal/sumweb => golang.org/x/mod/sumdb
cmd/go/internal/dirhash => golang.org/x/mod/sumdb/dirhash
cmd/go/internal/note => golang.org/x/mod/sumdb/note
cmd/go/internal/tlog => golang.org/x/mod/sumdb/tlog
When Russ copied these packages to x/mod, he added documentation and renamed some definitions. We should not undo that. At the same time, we should be careful to copy any changes and fixes to these packages from cmd/go to x/mod in a way that doesn't break compatibility.