Add parsing benchmark

crates/test_utils/src/bench_fixture.rs

@@ -1,7 +1,11 @@
 //! Generates large snippets of Rust code for usage in the benchmarks.
 
+use std::fs;
+
 use stdx::format_to;
 
+use crate::project_dir;
+
 pub fn big_struct() -> String {
     let n = 1_000;
 
@@ -26,3 +30,8 @@ struct S{} {{
 
     buf
 }
+
+pub fn glorious_old_parser() -> String {
+    let path = project_dir().join("bench_data/glorious_old_parser");
+    fs::read_to_string(&path).unwrap()
+}