Extract shortcuts loading logic from ChooserActivity

Extract shortcut loading logic from ChooserActivity into a new class
mostly as-is. Major changes:
- run the logic on a background executor and deliver the result on the
  main thread;
- replace dependencies from ChooserListAdapter with the data it
  provided.
A number of tests thap previusly used
ChooserListAdapter#addServiceResults to provide shortcut results into
the view are updated and re-enabled.

Test: manual tests
Test: atest IntentResolverUnitTests
Change-Id: Ia81cf9d0b0415fda1cfb53d45737a72f3fe540ff
11 files changed