proto: add ProtoPackageIsVersion4

Change-Id: I73a3da6d46e82c4c996ad9360e5b602efbbbcc83
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/218938
Reviewed-by: Damien Neil <[email protected]>

Author: dsnet

proto/deprecated.go

@@ -11,13 +11,6 @@ import (
 	"strconv"
 )
 
-// Deprecated: Do not use.
-const (
-	ProtoPackageIsVersion1 = true
-	ProtoPackageIsVersion2 = true
-	ProtoPackageIsVersion3 = true
-)
-
 var (
 	// Deprecated: No longer returned.
 	ErrNil = errors.New("proto: Marshal called with nil")

proto/proto.go

@@ -19,6 +19,13 @@ import (
 	"google.golang.org/protobuf/runtime/protoimpl"
 )
 
+const (
+	ProtoPackageIsVersion1 = true
+	ProtoPackageIsVersion2 = true
+	ProtoPackageIsVersion3 = true
+	ProtoPackageIsVersion4 = true
+)
+
 // Message is a protocol buffer message.
 type Message = protoiface.MessageV1