Remove dependencies from paging-runtime-uikit on multiplatformized paging-runtime classes

[veyndan]

PagingCollectionViewController's implementation currently mimics that of PagingDataAdapter. This is conceptually convenient when comparing implementations, but I'm doubtful that anyone actually does this (including myself since implementing this).

Having the implementations mimic each other requires a fair bit of multiplatformication overhead. PagingDataAdapter exists in paging-runtime, so therefore (unsurprisingly) depends on other paging-runtime classes (like AsyncPagingDataDiffer), and these classes in turn depend on some RecyclerView classes. All these dependencies of PagingDataAdapter required multiplatformizing, as can be seen here.

Instead of having to maintain a multiplatformized fork of paging-runtime, is it possible for paging-runtime-uikit to just use classes found in paging-common? For example, depending on PagingDataDiffer (found in paging-common) instead of AsyncPagingDataDiffer (found in paging-runtime).

CC @ianhanniballake @yigit @claraf3 @dlam @swankjesse