internal/value: rename the Unwrap method as ProtoUnwrap

Add a Proto prefix before the Unwrap method to reduce the probability that
it would ever conflict with a method of the same name that a
custom implementation of Enum, Message, List, or Map may have.

Change-Id: I628bf8335583f2747ab4589f3e6ff82e4501ce98
Reviewed-on: https://go-review.googlesource.com/c/151817
Reviewed-by: Herbie Ong <herbie@google.com>
diff --git a/internal/value/map.go b/internal/value/map.go
index db9656e..8505798 100644
--- a/internal/value/map.go
+++ b/internal/value/map.go
@@ -10,7 +10,10 @@
 	pref "github.com/golang/protobuf/v2/reflect/protoreflect"
 )
 
-func MapOf(p interface{}, kc, kv Converter) pref.Map {
+func MapOf(p interface{}, kc, kv Converter) interface {
+	pref.Map
+	Unwrapper
+} {
 	// TODO: Validate that p is a *map[K]V?
 	rv := reflect.ValueOf(p).Elem()
 	return mapReflect{rv, kc, kv}
@@ -75,12 +78,7 @@
 		}
 	}
 }
-func (ms mapReflect) Unwrap() interface{} {
+func (ms mapReflect) ProtoUnwrap() interface{} {
 	return ms.v.Addr().Interface()
 }
 func (ms mapReflect) ProtoMutable() {}
-
-var (
-	_ pref.Map  = mapReflect{}
-	_ Unwrapper = mapReflect{}
-)