PSS Task Switcher: Improve unit tests - Use real repositories

- Use real repositories and interactor in all tests
- The only fake parts are now the data sources: ActivityTaskManager and
  MediaProjectionManager.
  To make it easier to interact with them, there are now fake versions
  of those.

Bug: 286201261
Test: All unit tests under mediaprojection/taskswitcher/
Change-Id: I9a3732e26d9206f895cfe9f88a4329d67219c389