Add spacing information to delimiters.

This is an extension of the previous commit. It means the output of
something like this:
```
stringify!(let a: Vec<u32> = vec![];)
```
goes from this:
```
let a: Vec<u32> = vec![] ;
```
With this PR, it now produces this string:
```
let a: Vec<u32> = vec![];
```

compiler/rustc_lint/src/builtin.rs

@@ -1835,7 +1835,7 @@ impl KeywordIdents {
                         self.check_ident_token(cx, UnderMacro(true), ident);
                     }
                 }
-                TokenTree::Delimited(_, _, tts) => self.check_tokens(cx, tts),
+                TokenTree::Delimited(.., tts) => self.check_tokens(cx, tts),
             }
         }
     }