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.

Built from https://develop.svn.wordpress.org/trunk@28397


git-svn-id: http://core.svn.wordpress.org/trunk@28225 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Eliminate use of `extract()` in `wp_link_pages()`. 

Adds unit tests to a new file: `tests/post/template.php`. 
There were previously no unit tests for `wp_link_pages()`.
	
See #22400.

Built from https://develop.svn.wordpress.org/trunk@28398


git-svn-id: http://core.svn.wordpress.org/trunk@28226 1a063a9b-81f0-0310-95a4-ce76da25c4cd