To do this TaskVisualsChangedDelegate was added which multiplexes two listeners that are closely related.
Thumbnail overriding capabilities were also removed.
Fix: 342560598
Test: TaskVisualsChangedDelegateTest, TasksRepositoryTest
Flag: com.android.launcher3.enable_refactor_task_thumbnail
Change-Id: If065e4179cd1f15fe2cdf9b6bae51afcb57abcc6