reflect/protoregistry: add (*Types).Register{Message,Enum,Extension}

Add type-safe methods to register message, enum, and extension types.
Deprecate the NewTypes function and the (*Types).Register method.

Add (*File).RegisterFile and deprecate the NewFiles function and
the (*File).Register method.

Updates golang/protobuf#963

Change-Id: Ie89e77526e0874539e9bd929ca0ba8d758e65a6e
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/199898
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/internal/protolegacy/proto.go b/internal/protolegacy/proto.go
index ffca87a..b9f023a 100644
--- a/internal/protolegacy/proto.go
+++ b/internal/protolegacy/proto.go
@@ -61,7 +61,7 @@
 
 func RegisterType(m Message, s string) {
 	mt := protoimpl.X.LegacyMessageTypeOf(m, protoreflect.FullName(s))
-	if err := protoregistry.GlobalTypes.Register(mt); err != nil {
+	if err := protoregistry.GlobalTypes.RegisterMessage(mt); err != nil {
 		panic(err)
 	}
 }
@@ -75,7 +75,7 @@
 }
 
 func RegisterExtension(d *ExtensionDesc) {
-	if err := protoregistry.GlobalTypes.Register(d); err != nil {
+	if err := protoregistry.GlobalTypes.RegisterExtension(d); err != nil {
 		panic(err)
 	}
 }