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.

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git-svn-id: http://core.svn.wordpress.org/trunk@28225 1a063a9b-81f0-0310-95a4-ce76da25c4cd