Order grammar summary deterministically

In `load_grammar`, we were walking files in directory-entry order.
This may not be the same order in two places, leading to sections and
rules sorted in different orders in the grammar summary.  Let's sort
by file name so as to produce deterministic results.

Author: traviscross

tools/grammar/src/lib.rs

@@ -259,7 +259,7 @@ pub static GRAMMAR_RE: LazyLock<Regex> =
 pub fn load_grammar(diag: &mut Diagnostics) -> Grammar {
     let mut grammar = Grammar::default();
     let base = Path::new(env!("CARGO_MANIFEST_DIR")).join("../../src");
-    for entry in WalkDir::new(&base) {
+    for entry in WalkDir::new(&base).sort_by_file_name() {
         let entry = entry.unwrap();
         let path = entry.path();
         if path.extension().and_then(|s| s.to_str()) != Some("md") {