Eliminate use of `extract()` in `paginate_links()`. Adds unit tests. Moves `tests/general/template.php` (which only had one method) to `tests/general/paginateLinks.php`.

See #22400.


git-svn-id: https://develop.svn.wordpress.org/trunk@28397 602fd350-edb4-49c9-b593-d223f7449a82