Add minimal cube.ifcx example

cube.ifcx

@@ -0,0 +1,31 @@
+{
+  "header": {
+    "id": "ifc5.technical.buildingsmart.org/examples/Hello Wall/cube.ifcx",
+    "ifcxVersion": "ifcx_alpha",
+    "dataVersion": "1.0.0",
+    "author": "technical@buildingsmart.org",
+    "timestamp": "2024-06-01T00:00:00Z"
+  },
+  "schemas": {},
+  "data": [
+    {
+      "path": "cube-example-001",
+      "attributes": {
+        "usd::usdgeom::mesh": {
+          "faceVertexIndices": [
+            0, 1, 2, 0, 2, 3,
+            4, 5, 6, 4, 6, 7,
+            0, 1, 5, 0, 5, 4,
+            2, 3, 7, 2, 7, 6,
+            0, 3, 7, 0, 7, 4,
+            1, 2, 6, 1, 6, 5
+          ],
+          "points": [
+            [0, 0, 0], [1, 0, 0], [1, 1, 0], [0, 1, 0],
+            [0, 0, 1], [1, 0, 1], [1, 1, 1], [0, 1, 1]
+          ]
+        }
+      }
+    }
+  ]
+}