types: make Result an interface and move existing Result to separate package

pkg/version/legacy_examples/examples.go

@@ -23,6 +23,7 @@ import (
 	"sync"
 
 	"github.com/containernetworking/cni/pkg/types"
+	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/cni/pkg/version/testhelpers"
 )
 
@@ -114,8 +115,8 @@ func main() { skel.PluginMain(c, c) }
 //
 // As we change the CNI spec, the Result type and this value may change.
 // The text of the example plugins should not.
-var ExpectedResult = &types.Result{
-	IP4: &types.IPConfig{
+var ExpectedResult = &current.Result{
+	IP4: &current.IPConfig{
 		IP: net.IPNet{
 			IP:   net.ParseIP("10.1.2.3"),
 			Mask: net.CIDRMask(24, 32),