proto: move T->*T wrappers from internal/scalar to proto

Usage of these is pervasive in code which works with proto2, and proto2
will be with us for a long, long time to come. Move them to the proto
package.

Change-Id: I1b2e57429fd5a8f107a848a4492d20c27f304bd7
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/185543
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/encoding/prototext/other_test.go b/encoding/prototext/other_test.go
index 5b3376b..3ffa071 100644
--- a/encoding/prototext/other_test.go
+++ b/encoding/prototext/other_test.go
@@ -10,7 +10,6 @@
 	"google.golang.org/protobuf/encoding/prototext"
 	"google.golang.org/protobuf/internal/impl"
 	pimpl "google.golang.org/protobuf/internal/impl"
-	"google.golang.org/protobuf/internal/scalar"
 	"google.golang.org/protobuf/proto"
 	preg "google.golang.org/protobuf/reflect/protoregistry"
 
@@ -155,9 +154,9 @@
 		resolver: preg.NewTypes(),
 		message: func() proto.Message {
 			m := &pb2.Nested{
-				OptString: scalar.String("embedded inside Any"),
+				OptString: proto.String("embedded inside Any"),
 				OptNested: &pb2.Nested{
-					OptString: scalar.String("inception"),
+					OptString: proto.String("inception"),
 				},
 			}
 			b, err := proto.MarshalOptions{Deterministic: true}.Marshal(m)
@@ -176,9 +175,9 @@
 		resolver: preg.NewTypes(pimpl.Export{}.MessageTypeOf(&pb2.Nested{})),
 		message: func() *pb2.KnownTypes {
 			m := &pb2.Nested{
-				OptString: scalar.String("embedded inside Any"),
+				OptString: proto.String("embedded inside Any"),
 				OptNested: &pb2.Nested{
-					OptString: scalar.String("inception"),
+					OptString: proto.String("inception"),
 				},
 			}
 			b, err := proto.MarshalOptions{Deterministic: true}.Marshal(m)
@@ -201,7 +200,7 @@
 		}(),
 		message: func() *pb2.KnownTypes {
 			m1 := &pb2.Nested{
-				OptString: scalar.String("message inside Any of another Any field"),
+				OptString: proto.String("message inside Any of another Any field"),
 			}
 			b1, err := proto.MarshalOptions{Deterministic: true}.Marshal(m1)
 			if err != nil {