cmd/go: skip computing BuildInfo in go list unless it's needed
The only fields of the go list output that require BuildInfo to be
computed are the Stale and StaleReason fields. If a user explicitly
requests JSON fields and does not ask for Stale or StaleReason, skip
the computation of BuildInfo.
For #29666
Change-Id: Ie77581c44babedcb5cb7f3dc7d6ed1078b56eee4
Reviewed-on: https://go-review.googlesource.com/c/go/+/402736
Run-TryBot: Michael Matloob <matloob@golang.org> Reviewed-by: Michael Matloob <matloob@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Matloob <matloob@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>