Update grammar

Bounds are CONSTNESS ASYNCNESS POLARITY

Author: compiler-errors

crates/syntax/rust.ungram

@@ -614,7 +614,7 @@ TypeBoundList =
 
 TypeBound =
   Lifetime
-| ('?' | '~' 'const')? Type
+| ('~' 'const' | 'const')? 'async'? '?'? Type
 
 //************************//
 //        Patterns        //

crates/syntax/src/ast/generated/nodes.rs

@@ -1410,9 +1410,10 @@ pub struct TypeBound {
 }
 impl TypeBound {
     pub fn lifetime(&self) -> Option<Lifetime> { support::child(&self.syntax) }
-    pub fn question_mark_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![?]) }
     pub fn tilde_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![~]) }
     pub fn const_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![const]) }
+    pub fn async_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![async]) }
+    pub fn question_mark_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![?]) }
     pub fn ty(&self) -> Option<Type> { support::child(&self.syntax) }
 }