internal: replace AstTransformer with mutable syntax trees

crates/syntax/src/ted.rs

@@ -184,6 +184,9 @@ fn ws_between(left: &SyntaxElement, right: &SyntaxElement) -> Option<SyntaxToken
     if left.kind() == T![&] && right.kind() == SyntaxKind::LIFETIME {
         return None;
     }
+    if right.kind() == SyntaxKind::GENERIC_ARG_LIST {
+        return None;
+    }
 
     if right.kind() == SyntaxKind::USE {
         let mut indent = IndentLevel::from_element(left);