Caching clean up, remove dependency on old shared lib loading/caching logic

- Clarify caching policy, we only cache the last N task snapshots
- Pull out necessary logic from RecentsTaskLoadPlan (deprecated) into
  launcher class RecentTasksList which also manages the invalidation of
  the last loaded list
- Pull out logic from task loading logic in the shared lib into separate
  classes TaskThumbnailCache and TaskIconCache, and have each task view
  manage the load request for data

Bug: 117603579
Test: Thumbnails still load

Change-Id: I938e4dea19e7f5d24724c32194d254ca003e89aa