Provide more usable snapshots and retainingPath analysis tools like Eclipse Memory Analyzer.

The Eclipse Memory Analyzer
(https://help.eclipse.org/2020-09/index.jsp?topic=%2Forg.eclipse.mat.ui.help%2Fgettingstarted%2Fbasictutorial.html&cp%3D61_1_0) Have many features help developers to troubleshoot memory leaks.
The "merge shortest path to GC roots" feature is especially helpful for finding root causes of leaks.
AFAIK the retaining path method of vm_service basically returns a random path for now.

We should be able to implement similar functionality in devtools.

未指定文件或测试。首先检查 vm_service 的 retaining path 方法和 DevTools 的内存分析入口点，然后将所请求的行为与 Eclipse Memory Analyzer 的“merge shortest path to GC roots”功能进行比较；当 DevTools 提供可用于查找泄漏根的 snapshot 和 retaining-path 分析时，即表示完成。

由索引模型根据 Issue 内容生成。