Compare to remote file system (sftp) using VS Code API

[mprotasov]

We can implement comparing with remote files/folders using VS Code API and additional extension.
For SFTP it is SSH FS (https://marketplace.visualstudio.com/items?itemName=Kelvin.vscode-sshfs). Important - we should use v1.24.1 (as in H marketplace), latest 1.26.1 is slightly broken.

Proposed pipeline:

0. User has SSH FS installed on their VS Code
1. User calls command 'Compare with remote file/folder' and enters desired uri (e.g. ssh://user@localhost:2222/data/)
2. Message with pair of uris is sent to sudu-editor
3. For local folders/files, sudu-editor retrieve needed information (folder listing, file data, metadata) using existing node.js fs mechanism
4. For remote folders/files, sudu-editor calls method of FileAccessProvider, registered by VS Code extension. FileAccessProvider reads data using VS Code fs API and returns it to sudu-editor. Access to sftp (for example, password prompt) is handled on this step by SSH FS

I've tested SSH FS extension with various uris (folders and files), that do not belong to VS Code workspace. Everything seems to work fine