Fix a11y focus issue with partial scrolls and notifyDataSetChanged.

When using accessibility to navigate to an off-screen item, RecyclerView
would attempt to scroll the entire view to bring the next item to the
top. However, if there were insufficient items for a full scroll, and
the scroll triggered a notifyDataSetChanged call, RecyclerView would
incorrectly reset focus to the first visible item after the scroll.
Empirically, the notifyDataSetChanged is triggred by the icon loading.

The workaround for the issue is to make ChooserGridAdapter to invoke
notifyItemChange when the corresponded icon gets loaded.

Fix: 298193161
Test: manual testing
Flag: android.service.chooser.notify_single_item_change_on_icon_load
Change-Id: I6def9705e57122ae69c36d87f92cdb40b5439651