Add 2 methods to `WP_List_Table`, `->get_orderby()` and `->get_order()`. Override the methods in `WP_Posts_List_Table`.
`WP_Posts_List_Table` calls `wp_edit_posts_query()` in `->prepare_items()` which is a wrapper for `wp()`. As such, we can obtain `orderby` and `order` via `get_query_var()`, instead of the URL.
Fixes#25493.
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