build(rust): vendor rnix parser crate

third_party/crates/rnix-0.14.0/test_data/parser/success/let.expect

@@ -0,0 +1,20 @@
+NODE_ROOT@0..16
+  NODE_LET_IN@0..16
+    TOKEN_LET@0..3 "let"
+    TOKEN_WHITESPACE@3..4 " "
+    NODE_ATTRPATH_VALUE@4..11
+      NODE_ATTRPATH@4..5
+        NODE_IDENT@4..5
+          TOKEN_IDENT@4..5 "a"
+      TOKEN_WHITESPACE@5..6 " "
+      TOKEN_ASSIGN@6..7 "="
+      TOKEN_WHITESPACE@7..8 " "
+      NODE_LITERAL@8..10
+        TOKEN_INTEGER@8..10 "42"
+      TOKEN_SEMICOLON@10..11 ";"
+    TOKEN_WHITESPACE@11..12 " "
+    TOKEN_IN@12..14 "in"
+    TOKEN_WHITESPACE@14..15 " "
+    NODE_IDENT@15..16
+      TOKEN_IDENT@15..16 "a"
+