tamer: ir::xir::tree: Explicitly list unhandled tokens for exhaustiveness

This allows Rust to carry out its exhaustiveness check for when we add new
tokens.  It further ensure that we understand what we missed, or chose not
to handle.

DEV-10863

tamer/src/ir/xir/tree.rs

@@ -718,7 +718,9 @@ impl ParserState {
             Token::AttrValue(value, span) => stack.close_attr(value, span),
             Token::Text(value, span) => stack.text(value, span),
 
-            todo => Err(ParseError::Todo(todo, stack)),
+            Token::Comment(..) | Token::CData(..) | Token::Whitespace(..) => {
+                Err(ParseError::Todo(tok, stack))
+            }
         }
         .map(|new_stack| self.store_or_emit(new_stack))
     }