proposal: cmd/go: allow go get to choose versions based on the go version constraints

[hyangah]

With extended forwards compatibility feature (#57001), the go line in go.mod will prescribe the minimum go version required to compile the go module. If the work module says go 1.27 but a dependency says go 1.28, the work module should update its go.mod to require at least go 1.28.

https://go.googlesource.com/proposal/+/master/design/57001-gotoolchain.md#effect-in-dependencies

For library module maintainers who want to have better control of their minimum go version requirements, dependency update can be rather challenging. They have to pick the dependency version carefully to avoid bumping up their own modules' go version because one of their dependencies chose to bump their go version in their latest release.

We can think of various ways of helping users choose the right version such as

• extend the go list -m --versions to present the minimum required go version for each version.
• make pkgsite present the minimum required go version in its version view (which works only on open-source modules and not very convenient)

However, querying the requirement individually doesn't scale well when there are many dependencies.
It would be nice if the go get has an option to compute and choose the latest versions compatible with the given go version requirement.

[dmitshur]

CC @matloob, @bcmills.