Merge #48

48: Revert the visibility removal of macro_rules visibility (#46) r=Veykril a=ChayimFriedman2

As discussed in https://github.com/rust-analyzer/ungrammar/pull/46#issuecomment-1049758027.

Co-authored-by: Chayim Refael Friedman <chayimfr@gmail.com>
diff --git a/rust.ungram b/rust.ungram
index 6b31f98..572afe2 100644
--- a/rust.ungram
+++ b/rust.ungram
@@ -102,7 +102,7 @@
 | Use
 
 MacroRules =
-  Attr*
+  Attr* Visibility?
   'macro_rules' '!' Name
   TokenTree