move esnext tests into their own fixtures folder

test/fixtures/esnext/es6-spread/inside-function-expression.js

@@ -0,0 +1,10 @@
+var object = {
+  list: [],
+
+  append: function(...items) {
+    this.list.push(...items);
+  }
+};
+
+object.append(1, 2, ...[3, 4]);
+assert.deepEqual(object.list, [1, 2, 3, 4]);