[feature request] Click to copy

I'm using RDT to work on a mobile site, so I find difficult to read the server/client differences in the tool

I prefer to copy-paste them into another text editor to read.
It'd be nice if there were a faster way to copy/paste, since clicking and dragging highlights both the server text and client text together.

首先定位用於渲染 issue 中所述伺服器/用戶端差異的 RDT UI。新增一種無需同時選取兩側即可更快速複製所需文字的方式，然後驗證複製操作只會產生所選伺服器或用戶端的內容。

由索引模型根據 Issue 內容生成。