Offer the Date added (Newest) sort on every product list

[boo-code]

Questions	Answers
Description?	SearchProvider::getAvailableSortOrders() builds the date_add ("Date added" / newest) sort orders but only appends them when $query->getQueryType() == 'new-products', so category, manufacturer, supplier and search lists never offer a "newest" sort. Sorting by newest is one of the core product-list sorts in UX research (https://baymard.com/blog/current-state-product-list-and-filtering, "64% don't allow all 4: Price, User Rating, Best-Selling, Newest"). This moves the two date_add sort orders out of the new-products special case so they are available on every product list; Sales stays the default sort, so only the option is added, and the new-products page is unchanged. Fixes #1268.
Type?	improvement
BC breaks?	no
Deprecations?	no
Fixed ticket?	Fixes #1268
Sponsor company
How to test?	Open any category page: the sort dropdown now lists "Date added, oldest to newest" and "Date added, newest to oldest" alongside the existing options, and selecting the latter sorts by product.date_add.desc. Verified live on a 9.2 shop. php-cs-fixer clean; the change only relocates existing lines (no new symbols), and this module runs php-cs-fixer + PHPStan in CI (no PHPUnit job) — getAvailableSortOrders() is a private method not covered by the existing SearchProvider tests, which are unaffected.