This change adds the unique package for canonicalizing values, as
described by the proposal in #62483.
Fixes#62483.
Change-Id: I1dc3d34ec12351cb4dc3838a8ea29a5368d59e99
Reviewed-on: https://go-review.googlesource.com/c/go/+/574355
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ingo Oeser <nightlyone@googlemail.com>
Reviewed-by: David Chase <drchase@google.com>
