cmd/go/internal/modload: inject modfetch.Fetcher_ into commitRequirements

cmd/go/internal/modload: inject modfetch.Fetcher_ into commitRequirements

This commit continues the injection of the global Fetcher_ variable into
the various function calls that make use of it.  The purpose is to
prepare for the eventual removal of the global Fetcher_ variable and
eliminate global state within the modfetch package.

[git-generate]
cd src/cmd/go/internal/modload
rf '
  inject modfetch.Fetcher_ commitRequirements
  mv readModGraph.fetcher_ readModGraph.f
'

cd ../modfetch
sed -i '
  s/for _, f := range fetcher_.workspaceGoSumFiles {/for _, fn := range fetcher_.workspaceGoSumFiles {/
  s/fetcher_.sumState.w\[f\] = make(map\[module.Version\]\[\]string)/fetcher_.sumState.w[fn] = make(map[module.Version][]string)/
  s/_, err := readGoSumFile(fetcher_.sumState.w\[f\], f)/_, err := readGoSumFile(fetcher_.sumState.w[fn], fn)/
' fetch.go
rf '
  mv GoMod.fetcher_ GoMod.f
  mv GoMod Fetcher.GoMod
  mv readDiskGoMod.fetcher_ readDiskGoMod.f
  mv readDiskGoMod Fetcher.readDiskGoMod
  mv initGoSum.fetcher_ initGoSum.f
  mv initGoSum Fetcher.initGoSum
  mv HaveSum.fetcher_ HaveSum.f
  mv checkGoMod.fetcher_ checkGoMod.f
  mv checkModSum.fetcher_ checkModSum.f
  mv WriteGoSum.fetcher_ WriteGoSum.f
  mv WriteGoSum Fetcher.WriteGoSum
  mv Lookup.fetcher_ Lookup.f
  mv Lookup Fetcher.Lookup
'

Change-Id: Ifbe7d6b90b93fd65a7443434035921e6b42dea1c
Reviewed-on: https://go-review.googlesource.com/c/go/+/724241
Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@google.com>