feat: 拆分 stress benchmark 到细粒度单热点测试并修复 bench 采样逻辑

tests/stress/prop_bracket.js

@@ -0,0 +1,9 @@
+var ITERATIONS = 100000;
+
+var obj = { a: 1, b: 2, c: 3 };
+var sum = 0;
+for (var i = 0; i < ITERATIONS; i++) {
+  var x = obj["a"];
+  sum += x;
+}
+sum