cmd/go: annotate versions in vendor/modules.txt

In order to prevent edit wars with previous cmd/go releases,
the new version annotations are only included if the main module
specifies 'go 1.17' or higher.

Fixes #36876

Change-Id: Iba15e47dd1ac2c16d754679a9b501db4069fa250
Reviewed-on: https://go-review.googlesource.com/c/go/+/315409


Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>