Use xshell::read_file instead of fs::read_to_string

xtask/src/codegen/gen_parser_tests.rs

@@ -124,7 +124,7 @@ fn existing_tests(dir: &Path, ok: bool) -> Result<HashMap<String, (PathBuf, Test
             let file_name = path.file_name().unwrap().to_str().unwrap();
             file_name[5..file_name.len() - 3].to_string()
         };
-        let text = fs::read_to_string(&path)?;
+        let text = xshell::read_file(&path)?;
         let test = Test { name: name.clone(), text, ok };
         if let Some(old) = res.insert(name, (path, test)) {
             println!("Duplicate test: {:?}", old);