editor: Ensure correct tab icon is shown for files outside of the current project (#25933)

Closes #25885 

This PR improves the matching for file icons to tabs. 
Previously, the tab icon would be resolved based upon the relative path
in the current project. However, this caused the default file icon being
assigned to all files outside of the project, as the relative path for
these files would be empty.

Instead, `path_for_buffer` is now used which always returns a proper
file name even for paths outside the current project (as also stated [in
this
comment](https://github.com/zed-industries/zed/blob/fee9c677078ad5beebe151e8350e1fc353230dc9/crates/editor/src/items.rs#L1689)).
As the file name is sufficient for matching icons to files, this fixes
the linked issue whilst not changing anything for previously properly
matched icons.

| `main` | This PR |
| --- | --- | 
| <img width="296" alt="main"
src="https://github.com/user-attachments/assets/e72b8b5d-aa1c-4a8e-903f-14239f5b8764"
/> | <img width="296" alt="PR"
src="https://github.com/user-attachments/assets/a736974a-ce41-4861-be3f-95448cc7ffd0"
/> |

Release Notes:

- Fixed wrong file icons being shown for files outside of the current
project.

crates/editor/src/items.rs

@@ -618,11 +618,8 @@ impl Item for Editor {
         ItemSettings::get_global(cx)
             .file_icons
             .then(|| {
-                self.buffer
-                    .read(cx)
-                    .as_singleton()
-                    .and_then(|buffer| buffer.read(cx).project_path(cx))
-                    .and_then(|path| FileIcons::get_icon(path.path.as_ref(), cx))
+                path_for_buffer(&self.buffer, 0, true, cx)
+                    .and_then(|path| FileIcons::get_icon(path.as_ref(), cx))
             })
             .flatten()
             .map(Icon::from_path)