Clean up RelPath API (#38912)

Consolidate constructors and accessors.

Release Notes:

- N/A

---------

Co-authored-by: Cole Miller <cole@zed.dev>

crates/assistant_tools/src/edit_file_tool.rs

@@ -554,7 +554,7 @@ fn resolve_path(
                 .context("Can't create file: invalid filename")?;
 
             let new_file_path = parent_project_path.map(|parent| ProjectPath {
-                path: parent.path.join(RelPath::new(file_name).unwrap()),
+                path: parent.path.join(RelPath::unix(file_name).unwrap()),
                 ..parent
             });
 

crates/assistant_tools/src/list_directory_tool.rs

@@ -86,6 +86,7 @@ impl Tool for ListDirectoryTool {
         _window: Option<AnyWindowHandle>,
         cx: &mut App,
     ) -> ToolResult {
+        let path_style = project.read(cx).path_style(cx);
         let input = match serde_json::from_value::<ListDirectoryToolInput>(input) {
             Ok(input) => input,
             Err(err) => return Task::ready(Err(anyhow!(err))).into(),
@@ -100,7 +101,7 @@ impl Tool for ListDirectoryTool {
                 .filter_map(|worktree| {
                     worktree.read(cx).root_entry().and_then(|entry| {
                         if entry.is_dir() {
-                            Some(entry.path.as_str())
+                            Some(entry.path.display(path_style))
                         } else {
                             None
                         }