[release-branch.go1.17] cmd/go/internal/modload: scan dependencies of root...

[release-branch.go1.17] cmd/go/internal/modload: scan dependencies of root paths when raising version limits in editRequirements

Updates #47979
Fixes #48156

Change-Id: I1d9d854cda1378e20c70e6c6789b77e42e467ca7
Reviewed-on: https://go-review.googlesource.com/c/go/+/347290


Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
(cherry picked from commit 409434d6)
Reviewed-on: https://go-review.googlesource.com/c/go/+/348411