Update USD support in MuJoCo to Newton USD schemas v0.4.0.

See changelog for more info.

PiperOrigin-RevId: 960284190
Change-Id: I89a84b1efbc22c89ee99db7436851ef27a325176

plugin/usd_decoder/newton_tokens.cc

@@ -0,0 +1,23 @@
+// Copyright 2025 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "third_party/mujoco/plugin/usd_decoder/newton_tokens.h"
+#include <pxr/base/tf/staticTokens.h>
+#include <pxr/pxr.h>
+
+PXR_NAMESPACE_OPEN_SCOPE
+
+TF_DEFINE_PUBLIC_TOKENS(NewtonTokens, NEWTON_TOKENS);
+
+PXR_NAMESPACE_CLOSE_SCOPE