Search query var gets re-slashed in rebooted query

`WP_Query` calls `stripslashes()` on the `s` query var when parsing searches: https://github.com/WordPress/wordpress-develop/blob/eb06a59f536692e9499b89abd3f156ff56d3075e/src/wp-includes/class-wp-query.php#L1338-L1341

`ES_WP_Query` mimics this behavior in `\ES_WP_Query_Wrapper::parse_search()`, but `\ES_WP_Query_Shoehorn::reboot_query_vars()` puts the original `s` back into the query, causing the slashed string to be returned in `get_search_query()` and functions relying on it like `wp_get_document_title()`.