runtime/protoiface: move and rename XXX_Methods

This CL moves and renames the protoreflect.ProtoMessage.XXX_Methods
to protoreflect.Message.ProtoMethods.

Since one needs to obtain a protoreflect.Message now to get at
the fast-path methods, we modify the method signatures to take
in a protoreflect.Message instead of protoreflect.ProtoMessage.
Doing so also avoids the wrapper hack that was formerly done on
impl.messageReflectWrapper.

After this change the new protoc-gen-go no longer generates
any XXX fields or methods. All internal fields and methods are truly
hidden from the end-user.

name                                     old time/op    new time/op    delta
Wire/Unmarshal/google_message1_proto2-4    1.50µs ±10%    1.50µs ± 2%    ~     (p=0.483 n=10+9)
Wire/Unmarshal/google_message1_proto3-4    1.06µs ± 6%    1.06µs ± 4%    ~     (p=0.814 n=9+9)
Wire/Unmarshal/google_message2-4            734µs ±22%     689µs ±13%    ~     (p=0.133 n=10+9)
Wire/Marshal/google_message1_proto2-4       790ns ±46%     652ns ± 8%    ~     (p=0.590 n=10+9)
Wire/Marshal/google_message1_proto3-4       872ns ± 4%     857ns ± 3%    ~     (p=0.168 n=9+9)
Wire/Marshal/google_message2-4              232µs ±16%     221µs ± 3%  -4.75%  (p=0.014 n=9+9)
Wire/Size/google_message1_proto2-4          164ns ± 2%     167ns ± 4%  +1.87%  (p=0.046 n=9+10)
Wire/Size/google_message1_proto3-4          240ns ± 9%     229ns ± 1%  -4.81%  (p=0.000 n=9+8)
Wire/Size/google_message2-4                58.9µs ± 9%    59.6µs ± 2%  +1.23%  (p=0.040 n=9+9)

name                                     old alloc/op   new alloc/op   delta
Wire/Unmarshal/google_message1_proto2-4      912B ± 0%      912B ± 0%    ~     (all equal)
Wire/Unmarshal/google_message1_proto3-4      688B ± 0%      688B ± 0%    ~     (all equal)
Wire/Unmarshal/google_message2-4            470kB ± 0%     470kB ± 0%    ~     (p=0.215 n=10+10)
Wire/Marshal/google_message1_proto2-4        240B ± 0%      240B ± 0%    ~     (all equal)
Wire/Marshal/google_message1_proto3-4        224B ± 0%      224B ± 0%    ~     (all equal)
Wire/Marshal/google_message2-4             90.1kB ± 0%    90.1kB ± 0%    ~     (all equal)
Wire/Size/google_message1_proto2-4          0.00B          0.00B         ~     (all equal)
Wire/Size/google_message1_proto3-4          0.00B          0.00B         ~     (all equal)
Wire/Size/google_message2-4                 0.00B          0.00B         ~     (all equal)

name                                     old allocs/op  new allocs/op  delta
Wire/Unmarshal/google_message1_proto2-4      24.0 ± 0%      24.0 ± 0%    ~     (all equal)
Wire/Unmarshal/google_message1_proto3-4      6.00 ± 0%      6.00 ± 0%    ~     (all equal)
Wire/Unmarshal/google_message2-4            8.49k ± 0%     8.49k ± 0%    ~     (all equal)
Wire/Marshal/google_message1_proto2-4        1.00 ± 0%      1.00 ± 0%    ~     (all equal)
Wire/Marshal/google_message1_proto3-4        1.00 ± 0%      1.00 ± 0%    ~     (all equal)
Wire/Marshal/google_message2-4               1.00 ± 0%      1.00 ± 0%    ~     (all equal)
Wire/Size/google_message1_proto2-4           0.00           0.00         ~     (all equal)
Wire/Size/google_message1_proto3-4           0.00           0.00         ~     (all equal)
Wire/Size/google_message2-4                  0.00           0.00         ~     (all equal)

Change-Id: Ibf3263ad0f293326695c22020a92a6b938ef4f65
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/185697
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/message_reflect.go b/internal/impl/message_reflect.go
index a9eb7a9..c79b55a 100644
--- a/internal/impl/message_reflect.go
+++ b/internal/impl/message_reflect.go
@@ -11,7 +11,6 @@
 	"google.golang.org/protobuf/internal/pragma"
 	pvalue "google.golang.org/protobuf/internal/value"
 	pref "google.golang.org/protobuf/reflect/protoreflect"
-	piface "google.golang.org/protobuf/runtime/protoiface"
 )
 
 // MessageState is a data structure that is nested as the first field in a
@@ -81,8 +80,8 @@
 }
 
 type (
-	messageIfaceWrapper   messageDataType
 	messageReflectWrapper messageDataType
+	messageIfaceWrapper   messageDataType
 )
 
 var (
@@ -112,33 +111,9 @@
 func (m *messageIfaceWrapper) ProtoReflect() pref.Message {
 	return (*messageReflectWrapper)(m)
 }
-func (m *messageIfaceWrapper) XXX_Methods() *piface.Methods {
-	// TODO: Consider not recreating this on every call.
-	m.mi.init()
-	return &piface.Methods{
-		Flags:         piface.MethodFlagDeterministicMarshal,
-		MarshalAppend: m.marshalAppend,
-		Unmarshal:     m.unmarshal,
-		Size:          m.size,
-		IsInitialized: m.isInitialized,
-	}
-}
 func (m *messageIfaceWrapper) ProtoUnwrap() interface{} {
 	return m.p.AsIfaceOf(m.mi.GoType.Elem())
 }
-func (m *messageIfaceWrapper) marshalAppend(b []byte, _ pref.ProtoMessage, opts piface.MarshalOptions) ([]byte, error) {
-	return m.mi.marshalAppendPointer(b, m.p, newMarshalOptions(opts))
-}
-func (m *messageIfaceWrapper) unmarshal(b []byte, _ pref.ProtoMessage, opts piface.UnmarshalOptions) error {
-	_, err := m.mi.unmarshalPointer(b, m.p, 0, newUnmarshalOptions(opts))
-	return err
-}
-func (m *messageIfaceWrapper) size(msg pref.ProtoMessage) (size int) {
-	return m.mi.sizePointer(m.p, 0)
-}
-func (m *messageIfaceWrapper) isInitialized(_ pref.ProtoMessage) error {
-	return m.mi.isInitializedPointer(m.p)
-}
 
 type extensionMap map[int32]ExtensionField