Refactor `PagingAndSortingRepository` and its reactive variants into fragment interfaces

[mp911de]

With the introduction of repository fragments in Spring Data 2.0, we introduced fragments as the primary means for feature extensions. PagingAndSortingRepository, ReactiveSortingRepository, and RxJava3SortingRepository are subclasses of a CRUD repository and therefore limited in composition.

We want to cut the dependency to CRUD repository to not require using paging/sorting functionality to expose CRUD methods. The paging repository interfaces would subclass Repository only along with type variables for the domain type and identifier type.