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

tests/stress/call_this.js

@@ -0,0 +1,13 @@
+var ITERATIONS = 20000;
+
+var obj = {
+  value: 10,
+  getValue: function () { return this.value; },
+  setValue: function (v) { this.value = v; return this; }
+};
+var sum = 0;
+for (var i = 0; i < ITERATIONS; i++) {
+  obj.setValue(i);
+  sum += obj.getValue();
+}
+sum