Improve suggestion for tuple struct pattern matching errors.

Currently, when a user uses a struct pattern to pattern match on
a tuple struct, the errors we emit generally suggest adding fields
using their field names, which are numbers. However, numbers are
not valid identifiers, so the suggestions, which use the shorthand
notation, are not valid syntax. This commit changes those errors
to suggest using the actual tuple struct pattern syntax instead,
which is a more actionable suggestion.

compiler/rustc_parse/src/parser/mod.rs

@@ -932,7 +932,7 @@ impl<'a> Parser<'a> {
             self.bump();
             Ok(Ident::new(symbol, self.prev_token.span))
         } else {
-            self.parse_ident_common(false)
+            self.parse_ident_common(true)
         }
     }