Fixing Launcher preview leaking surface and memory

> Closing existing preview if a new request comes for same host token
> Closing in-memory icon db when closing preview
> Removing unnecessary wait blocks on UI thread and rendering
  view asynchronously
> Fixing preview loading failing on LauncherAppState access

Bug: 186712316
Bug: 187140897
Test: Manual
Change-Id: I045930b007e5dc015320224a197eee20a8354d17