Support virtual workspaces

👋 Hi there, Martin here, from the VS Code team.

Recently we've announced the [Remote Repository feature](https://code.visualstudio.com/updates/v1_56#_remote-repositories-remotehub) that lets you browse and edit files and folders directly on GitHub.

`Open Remote Repository...` opens VSCode on a folder or workspace located on a virtual file system. We call this a **virtual workspace**. We observed that not all extension support this well, either because they can not, or they haven't thought about it.

It would be fantastic if you could test whether your extension can handle virtual workspaces:

Check out the [Virtual Workspaces Extension Author Guide](https://github.com/microsoft/vscode/wiki/Virtual-Workspaces) on how to do that.

When done, set the new `virtualWorkspaces` capability in your 'package.json'.

```
{
"capabilities": {
"virtualWorkspaces": true | false
}
}
```

- Use `"virtualWorkspaces": true` if your extension is prepared for virtual workspaces
- Use `"virtualWorkspaces": false` if your extension should be disabled when a virtual workspace is opened

For questions and comments please use the [Virtual Workspaces Tracking Issue](https://github.com/microsoft/vscode/issues/123115).

Thanks for the support and the great work! ❤️