Add MjcPhysicsSceneAPI support.

Still missing compiler settings but will follow up in a future CL. Tried to add full coverage for testing setting of attributes to non-default values.

PiperOrigin-RevId: 761636862
Change-Id: Id4b9486645b2600931556cdcb8dc71f28ec309cd

test/experimental/usd/test_utils.h

@@ -74,7 +74,7 @@ pxr::SdfLayerRefPtr LoadLayer(
     const pxr::SdfFileFormat::FileFormatArguments& args = {});
 
 template <typename T>
-void ExpectAttributeEqual(pxr::UsdStageRefPtr stage, const char* path,
+void ExpectAttributeEqual(pxr::UsdStageRefPtr stage, pxr::SdfPath path,
                           const T& value) {
   auto attr = stage->GetAttributeAtPath(pxr::SdfPath(path));
   EXPECT_TRUE(attr.IsValid()) << "Attribute " << path << " is not valid";
@@ -84,13 +84,19 @@ void ExpectAttributeEqual(pxr::UsdStageRefPtr stage, const char* path,
                                << attr_value << ". Expected: " << value;
 }
 
+template <typename T>
+void ExpectAttributeEqual(pxr::UsdStageRefPtr stage, const char* path,
+                          const T& value) {
+  ExpectAttributeEqual(stage, pxr::SdfPath(path), value);
+}
+
 // Specialization for SdfAssetPath, so that we can compare only the asset path
 // and not care about whatever the resolved path is.
 // Otherwise the default operator== would fail because it tests for equality of
 // the asset path AND the resolved path.
 template <>
 void ExpectAttributeEqual<pxr::SdfAssetPath>(pxr::UsdStageRefPtr stage,
-                                             const char* path,
+                                             pxr::SdfPath,
                                              const pxr::SdfAssetPath& value);
 
 void ExpectAttributeHasConnection(pxr::UsdStageRefPtr stage, const char* path,