feat: enable it to open multiple files

[CatBraaain]

Enable it to open multiple files

It's possible to get all selected files when running open command from context menu on explorer. Here is a related code snippet on Stack Overflow:

• VS Code extension api get all selected files
• How to obtain a list of selected files from the explorer pane of VS Code?

Test

1. Select two text files.
2. Run open command from context menu.
3. Two text files opened.

I'm very new to pull request, I welcome any feedback.