cmd/go: add setters for critical State fields

cmd/go: add setters for critical State fields

This commit unexports critical State fields and provides setter
methods to update their values.

[git-generate]
cd src/cmd/go/internal/modfetch
rf '
  add fetch.go:490 var jitsu int = 0 // rf marker
  mv State.GoSumFile State.GoSumFile_
  mv State.WorkspaceGoSumFiles State.WorkspaceGoSumFiles_
  add jitsu \
    func (s *State) GoSumFile() string { \
      return ""
    } \
    \
    func (s *State) SetGoSumFile(str string) { \
    } \
    \
    func (s *State) AddWorkspaceGoSumFile(file string) { \
        s.WorkspaceGoSumFiles_ = append(s.WorkspaceGoSumFiles_, file) \
    }
    \

  ex {
    var s *State
    var x string
    s.GoSumFile_ = x -> s.SetGoSumFile(x)
  }

  rm jitsu
'

cd ../modload
sed -i '
  s/modfetch.ModuleFetchState.WorkspaceGoSumFiles_ = append(modfetch.ModuleFetchState.WorkspaceGoSumFiles_, sumFile)/modfetch.ModuleFetchState.AddWorkspaceGoSumFile(sumFile)/
' init.go

for dir in modcmd modload ; do
 cd ../${dir}
 rf '
   ex {
     import "cmd/go/internal/modfetch"
     var s *modfetch.State
     var x string
     s.GoSumFile_ = x -> s.SetGoSumFile(x)
   }
 '
done

cd ../modfetch
rf '
 mv State.GoSumFile_ State.goSumFile
 mv State.WorkspaceGoSumFiles_ State.workspaceGoSumFiles
 add State.GoSumFile: return s.goSumFile
 rm State.GoSumFile://+1
 add State.SetGoSumFile: s.goSumFile = str
'

Change-Id: Iff694aad7ad1cc62d2096c210dbaa3cce2b4061d
Reviewed-on: https://go-review.googlesource.com/c/go/+/720840
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>