build(rust): vendor rnix parser crate

third_party/crates/rnix-0.14.0/test_data/parser/success/trivia.nix

@@ -0,0 +1,9 @@
+{
+  add = /* the first value */ x: /* the second value */ y: x + y;
+  string = /* meaning of life */ "42";
+    hi = 3.0000000;
+ # Store my password in plain text
+      password  =      "hunter2";
+}
+   # trailing
+       # comments