Fix git features not working when a Windows host collaborates with a unix guest (#43515)

We were using `std::path::Path::strip_prefix` to determine which
repository an absolute path belongs to, which doesn't work when the
paths are Windows-style but the code is running on unix. Replace it with
a platform-agnostic implementation of `strip_prefix`.

Release Notes:

- Fixed git features not working when a Windows host collaborates with a
unix guest

crates/project_panel/src/project_panel.rs

@@ -4837,7 +4837,7 @@ impl ProjectPanel {
                                         .collect::<Vec<_>>();
                                     let active_index = folded_ancestors.active_index();
                                     let components_len = components.len();
-                                    let delimiter = SharedString::new(path_style.separator());
+                                    let delimiter = SharedString::new(path_style.primary_separator());
                                     for (index, component) in components.iter().enumerate() {
                                         if index != 0 {
                                                 let delimiter_target_index = index - 1;