Canonicalize paths when running tests (#23655)

In the Windows test environment, the paths generated by `temp_tree()`
are symlink paths, which causes certain tests to fail.

I later noticed that when opening a project, we seem to always use
`canonicalize` to normalize the paths, as shown here:
https://github.com/zed-industries/zed/pull/21039.

This PR adopts a similar approach for the test environment to address
the issue.

Release Notes:

- N/A

crates/util/src/test.rs

@@ -11,10 +11,26 @@ use tempfile::TempDir;
 pub use assertions::*;
 pub use marked_text::*;
 
-pub fn temp_tree(tree: serde_json::Value) -> TempDir {
-    let dir = TempDir::new().unwrap();
-    write_tree(dir.path(), tree);
-    dir
+pub struct TempTree {
+    _temp_dir: TempDir,
+    path: PathBuf,
+}
+
+impl TempTree {
+    pub fn new(tree: serde_json::Value) -> Self {
+        let dir = TempDir::new().unwrap();
+        let path = std::fs::canonicalize(dir.path()).unwrap();
+        write_tree(path.as_path(), tree);
+
+        Self {
+            _temp_dir: dir,
+            path,
+        }
+    }
+
+    pub fn path(&self) -> &Path {
+        self.path.as_path()
+    }
 }
 
 fn write_tree(path: &Path, tree: serde_json::Value) {