Unloading thumbnails from task views once recents is hidden

- Re-enabling the high res thumbnail loader, ensuring that we clean up
  the visible recent tasks when the associated views are removed
- When the recents state is re-entered, we will trigger the loading of
  the data anew (which will usually just fetch data from the existing
  cache if launcher was not stopped)

Bug: 74537246
Change-Id: I9cd69015461e1de34b4b65faeb9adb8aebd1dd3d