Add a cache loading helper to synchronize cache loads and invalidations

With basically all caches in XWiki we have the situation that we need to prevent loading outdated data from before a cache invalidation. While some caches have custom solutions for it, others are lacking it, see XWIKI-23055. This issue is about introducing a generic and flexible helper for cache loading to make it easy to avoid that caches store outdated data. At the same time, the helper should avoid repeated computation of cache values by sharing the value between several loads that are running in parallel.