Explicitly override RemoteMediator.initialize with instructional comment

Fix + add transformation example to PagingSample tests

Renamed CheeseItem to CheeseListITem
Fix imports
Minor nits

Added an example of mock differ + mock paging source style viewmodel
test, which allows testing against separator / transformation logic.

Introduce local extensino functions for conditional chaining.

Update PagingSample with ViewBinding and ActivityScenario

A test uses local resources. That's why we can't
use applicationContext here.

Re-enable PagingWithNetwork tests in CI

Fix GithubBrowserSample

fragment-testing:1.2.x has a strict version dependency on
androidx.test.core 1.2.x, preventing upgrading to 1.3.x

Update paging sample to alpha13