internal/impl: rename MessageType as MessageInfo

The name MessageType is easily confused with protoreflect.MessageType.
Rename it as MessageInfo, which follows the pattern set by v1,
where the equivalent data structure is called InternalMessageInfo.

Change-Id: I535956e1f7c6e9b07e9585e889d5e93388d0d2ce
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/178478
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/encode_field.go b/internal/impl/encode_field.go
index 6dbbed1..2e4884d 100644
--- a/internal/impl/encode_field.go
+++ b/internal/impl/encode_field.go
@@ -70,13 +70,13 @@
 }
 
 func makeMessageFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
-	if fi, ok := getMessageType(ft); ok {
+	if fi, ok := getMessageInfo(ft); ok {
 		return pointerCoderFuncs{
 			size: func(p pointer, tagsize int, opts marshalOptions) int {
-				return sizeMessageType(p, fi, tagsize, opts)
+				return sizeMessageInfo(p, fi, tagsize, opts)
 			},
 			marshal: func(b []byte, p pointer, wiretag uint64, opts marshalOptions) ([]byte, error) {
-				return appendMessageType(b, p, wiretag, fi, opts)
+				return appendMessageInfo(b, p, wiretag, fi, opts)
 			},
 		}
 	} else {
@@ -93,11 +93,11 @@
 	}
 }
 
-func sizeMessageType(p pointer, mi *MessageType, tagsize int, opts marshalOptions) int {
+func sizeMessageInfo(p pointer, mi *MessageInfo, tagsize int, opts marshalOptions) int {
 	return wire.SizeBytes(mi.sizePointer(p.Elem(), opts)) + tagsize
 }
 
-func appendMessageType(b []byte, p pointer, wiretag uint64, mi *MessageType, opts marshalOptions) ([]byte, error) {
+func appendMessageInfo(b []byte, p pointer, wiretag uint64, mi *MessageInfo, opts marshalOptions) ([]byte, error) {
 	b = wire.AppendVarint(b, wiretag)
 	b = wire.AppendVarint(b, uint64(mi.sizePointer(p.Elem(), opts)))
 	return mi.marshalAppendPointer(b, p.Elem(), opts)
@@ -129,7 +129,7 @@
 }
 
 func makeGroupFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
-	if fi, ok := getMessageType(ft); ok {
+	if fi, ok := getMessageInfo(ft); ok {
 		return pointerCoderFuncs{
 			size: func(p pointer, tagsize int, opts marshalOptions) int {
 				return sizeGroupType(p, fi, tagsize, opts)
@@ -152,11 +152,11 @@
 	}
 }
 
-func sizeGroupType(p pointer, mi *MessageType, tagsize int, opts marshalOptions) int {
+func sizeGroupType(p pointer, mi *MessageInfo, tagsize int, opts marshalOptions) int {
 	return 2*tagsize + mi.sizePointer(p.Elem(), opts)
 }
 
-func appendGroupType(b []byte, p pointer, wiretag uint64, mi *MessageType, opts marshalOptions) ([]byte, error) {
+func appendGroupType(b []byte, p pointer, wiretag uint64, mi *MessageInfo, opts marshalOptions) ([]byte, error) {
 	b = wire.AppendVarint(b, wiretag) // start group
 	b, err := mi.marshalAppendPointer(b, p.Elem(), opts)
 	b = wire.AppendVarint(b, wiretag+1) // end group
@@ -190,7 +190,7 @@
 }
 
 func makeMessageSliceFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
-	if fi, ok := getMessageType(ft); ok {
+	if fi, ok := getMessageInfo(ft); ok {
 		return pointerCoderFuncs{
 			marshal: func(b []byte, p pointer, wiretag uint64, opts marshalOptions) ([]byte, error) {
 				return appendMessageSliceInfo(b, p, wiretag, fi, opts)
@@ -210,7 +210,7 @@
 	}
 }
 
-func sizeMessageSliceInfo(p pointer, mi *MessageType, tagsize int, opts marshalOptions) int {
+func sizeMessageSliceInfo(p pointer, mi *MessageInfo, tagsize int, opts marshalOptions) int {
 	s := p.PointerSlice()
 	n := 0
 	for _, v := range s {
@@ -219,7 +219,7 @@
 	return n
 }
 
-func appendMessageSliceInfo(b []byte, p pointer, wiretag uint64, mi *MessageType, opts marshalOptions) ([]byte, error) {
+func appendMessageSliceInfo(b []byte, p pointer, wiretag uint64, mi *MessageInfo, opts marshalOptions) ([]byte, error) {
 	s := p.PointerSlice()
 	var nerr errors.NonFatal
 	var err error
@@ -280,7 +280,7 @@
 }
 
 func makeGroupSliceFieldCoder(fd pref.FieldDescriptor, ft reflect.Type) pointerCoderFuncs {
-	if fi, ok := getMessageType(ft); ok {
+	if fi, ok := getMessageInfo(ft); ok {
 		return pointerCoderFuncs{
 			size: func(p pointer, tagsize int, opts marshalOptions) int {
 				return sizeGroupSliceInfo(p, fi, tagsize, opts)
@@ -326,7 +326,7 @@
 	return b, nerr.E
 }
 
-func sizeGroupSliceInfo(p pointer, mi *MessageType, tagsize int, opts marshalOptions) int {
+func sizeGroupSliceInfo(p pointer, mi *MessageInfo, tagsize int, opts marshalOptions) int {
 	s := p.PointerSlice()
 	n := 0
 	for _, v := range s {
@@ -335,7 +335,7 @@
 	return n
 }
 
-func appendGroupSliceInfo(b []byte, p pointer, wiretag uint64, mi *MessageType, opts marshalOptions) ([]byte, error) {
+func appendGroupSliceInfo(b []byte, p pointer, wiretag uint64, mi *MessageInfo, opts marshalOptions) ([]byte, error) {
 	s := p.PointerSlice()
 	var nerr errors.NonFatal
 	var err error