This commit partially reverts rust-lang#3934, opting to create a span that covers
the entire body of a closure when formatting a closure body with a
block-formatting strategy, rather than having the block-formatting code
determine if the visitor pointer should be rewound. The problem with
rewinding the visitor pointer is it may be incorrect for other (i.e.
non-artificial) AST nodes, as in the case of rust-lang#4382.

Closes rust-lang#4382

* Added test cases

* Fixed if condition comment issue

* Fixed extern C issue

* Removed previous test case

* Removed tmp file

* honor the authors intent

* Changed the file name to its original name

* Removed extra whitespace