Move canonicalize out of generated code

c++/src/capnp/canonicalize-test.c++

@@ -37,7 +37,7 @@ KJ_TEST("canonicalize yields cannonical message") {
 
   initTestMessage(root);
 
-  root.asReader().canonicalize();
+  canonicalize(root.asReader());
   //Will assert if canonicalize failed to do so
 }
 
@@ -141,7 +141,7 @@ KJ_TEST("upgraded lists can be canonicalized") {
   SegmentArrayMessageReader upgraded(kj::arrayPtr(segments, 1));
 
   auto root = upgraded.getRoot<TestLists>();
-  root.canonicalize();
+  canonicalize(root);
 }
 
 KJ_TEST("isCanonical requires truncation of 0-valued struct fields in all list members") {

c++/src/capnp/compiler/capnpc-c++.c++

@@ -1747,10 +1747,6 @@ private:
         "    return _reader.totalSize().asPublic();\n"
         "  }\n"
         "\n"
-        "  ::kj::Array<::capnp::word> canonicalize() {\n"
-        "    return _reader.canonicalize();\n"
-        "  }\n"
-        "\n"
         "#if !CAPNP_LITE\n"
         "  inline ::kj::StringTree toString() const {\n"
         "    return ::capnp::_::structString(_reader, *_capnpPrivate::brand);\n"

c++/src/capnp/message.h

@@ -498,6 +498,11 @@ static typename Type::Reader defaultValue() {
   return typename Type::Reader(_::StructReader());
 }
 
+template <typename T>
+kj::Array<word> canonicalize(T&& reader) {
+    return _::PointerHelpers<FromReader<T>>::getInternalReader(reader).canonicalize();
+}
+
 }  // namespace capnp
 
 #endif  // CAPNP_MESSAGE_H_