cmd/go: implement "go build -json"

cmd/go: implement "go build -json"

This adds support for a "-json" flag in all build-related go
subcommands. This causes build output and build failures to be
reported to stdout in a machine-readable way.

For #62067.
Fixes #23037.

Change-Id: Id045c5bd5dde9d16cc09dde6248a4b9637896a30
Reviewed-on: https://go-review.googlesource.com/c/go/+/536397
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Russ Cox <rsc@golang.org>