Make defaulting part of versioning codec

Most normal codec use should perform defaulting. DirectCodecs should not
perform defaulting. Update the defaulting_test to fuzz the list of known
defaulters. Use the new versioning.NewDefaultingCodec() method.

pkg/runtime/codec.go

@@ -76,6 +76,24 @@ func EncodeOrDie(e Encoder, obj Object) string {
 	return string(bytes)
 }
 
+// DefaultingSerializer invokes defaulting after decoding.
+type DefaultingSerializer struct {
+	Defaulter ObjectDefaulter
+	Decoder   Decoder
+	// Encoder is optional to allow this type to be used as both a Decoder and an Encoder
+	Encoder
+}
+
+// Decode performs a decode and then allows the defaulter to act on the provided object.
+func (d DefaultingSerializer) Decode(data []byte, defaultGVK *unversioned.GroupVersionKind, into Object) (Object, *unversioned.GroupVersionKind, error) {
+	obj, gvk, err := d.Decoder.Decode(data, defaultGVK, into)
+	if err != nil {
+		return obj, gvk, err
+	}
+	d.Defaulter.Default(obj)
+	return obj, gvk, nil
+}
+
 // UseOrCreateObject returns obj if the canonical ObjectKind returned by the provided typer matches gvk, or
 // invokes the ObjectCreator to instantiate a new gvk. Returns an error if the typer cannot find the object.
 func UseOrCreateObject(t ObjectTyper, c ObjectCreater, gvk unversioned.GroupVersionKind, obj Object) (Object, error) {