Copy path as Unix

### Description of the new feature / enhancement

Add "Copy path as Unix" in the right-click menu of File Explorer. When clicking on a file, you can copy the file's Unix format path (e.g. "/mnt/c/file.txt" or "/home/username/file.txt"). When clicking on an empty space, you can copy the Unix path of the containing folder (e.g. "/home/username").

### Scenario when this would be used?

This feature will be very convenient when you need to use File Explorer and WSL together.

### Supporting information

_No response_

The issue names File Explorer's right-click menu and WSL scenarios but no repository files, tests, or entry points. Start by locating the existing File Explorer context-menu integration and any copy-path behavior, then verify file and containing-folder cases produce the requested Unix paths.

Written by the indexing model from the issue text.