Fix copy pasta
Update `WP_CLI\Utils\load_command()` to handle commands like `sidebar widget`

Previously, `load_command()` only supported commands where the name matched exactly (e.g. `wp post` and `post.php`). The `* meta` commands escaped this by defining their classes within the parent class file.

This change means `wp sidebar widget` will resolve to `sidebar-widget.php`, as well as `sidebar.php`
Introduce `wp sidebar widget` with list, update, and remove