fetch and update shortcut icons in background thread

Bug: 141568904
Test: Manually verified use cases from following call-site (with and
without delay)

LauncherAppsCompatVO
  1. (Custom Shortcut) Long click on google maps -> widgets ->
     drag driving mode to workspace.
  2. Open chrome -> add to home screen -> add -> add automatically.

InstallShortcutReceiver
  Removed the line that trigger above flow for android O and above,
  then open chrome -> add to home screen -> add -> add automatically.

ShortcutDragPreviewProvider
  qdb -> long press on suggested app that has deep shortcut -> drag
  to workspace.

Change-Id: I59a4d004913a8df697af1fcfe0a080b6da01eefd