cmd: update x/tools to 59ff18c

cmd: update x/tools to 59ff18c

	$ go get golang.org/x/tools@59ff18c
	$ GOWORK=off go mod tidy
	$ GOWORK=off go mod vendor

This implies golang.org/x/sys@v0.38.0, for which I have also
updated src/go.mod for consistency.

I also upgraded x/mod@3f03020 to bring in some fixes to
code that go vet would otherwise have flagged in this CL.

This brings in a number of fixes and improvements to the analysis
tools within cmd/fix, which I will apply to std and cmd presently.

For golang/go#71859

Change-Id: I56c49e7ab28eb6ba55408a3721e9a898ee3067a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/719760
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>