x/tools/cmd/goimports: prefer rand/v2 where applicable

[findleyr]

cmd/goimports and gopls' goimports integration do not select rand/v2 in the following scenario, resulting in a type error:

package main

import (
	"fmt"
	"math/rand"
)

func main() {
	fmt.Println(rand.Perm())
}

https://go.dev/play/p/pNTZiwDiG8F

This issue is related to #58382 and #41800, where the goimports does not prefer a the latest version of a module. However, goimports treats standard library packages differently, and so this bug will require a separate fix.

[gopherbot]

Change https://go.dev/cl/573075 mentions this issue: imports: prefer math/rand/v2 over math/rand