✨ Drag and Drop "keep both files" prompt

### Is your feature request related to a problem? Please describe.

When user drags and drops a file, user doesn't have option to rename dragged file in case there is a duplicate file of the same name

### Describe the solution you'd like

In the alert telling the user that there exists duplicate files of the same name when dragging and dropping, add a button: `keep both` which will move the files and append `copy` to the end of the dragged files name
ex: `test.txt -> test copy.txt`

### Describe alternatives you've considered

n/a

### Additional context

Prerequisites:

* https://github.com/CodeEditApp/CodeEdit/issues/1018
* https://github.com/CodeEditApp/CodeEdit/pull/1031

先查看 issue #1018 和 pull request #1031，以了解现有的拖放重复文件流程。找到此 issue 中描述的 alert，然后添加并验证“保留两者”行为，包括所请求的文件名后缀“copy”。

由索引模型根据 Issue 内容生成。