Update post date when job listing is approved

It has been requested (1689684-zen) that we update the post date to the day the post is approved upon approval. Their reason for this is it may cause confusion when a new post shows up but the relative datestamp is "posted 2 days ago."

This makes sense to me. We could put it behind a filter if we think some people will want to maintain the initial posted date.

For now, this snippet will add the functionality:
```php
add_action( 'pending_to_publish', function( $post ) {
if ( 'job_listing' !== $post->post_type ) {
return;
}
$post_date = current_time( 'mysql' );
wp_update_post( array(
'ID' => $post->ID,
'post_date' => $post_date,
'post_date_gmt' => get_gmt_from_date( $post_date ),
) );
} );
```

Start by locating the job listing approval flow and the pending_to_publish hook in the plugin. Compare that flow with the provided snippet and verify that approving a job_listing updates its post date while other post types remain unchanged; the work is done when the approved listing shows the approval date.

Written by the indexing model from the issue text.