cmd/go: change error message for missing import with unused replacement
In readonly mode, if a package is not provided by any module in the
build list, and there is an unused replacement that contains the
package, we now recommend a 'go get' command to add a requirement on
the highest replaced version.
Fixes #41416
Change-Id: Iedf3539292c70ea6ba6857433fd184454d9325da
Reviewed-on: https://go-review.googlesource.com/c/go/+/263146
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: Bryan C. Mills <bcmills@google.com>
Trust: Jay Conrod <jayconrod@google.com>