Add isEmpty info in SplitInfo

Currently SplitInfo callback didn't dispatched if the top Activity is
from other process than TaskFragmentOrganizer's.

This CL adds a flag isEmpty in SplitInfo to make users know if there may
be an Activity from other process even if Activity list is empty.

Bug: 202230350
Test: manual - reproducible steps mentioned in bug 202230350
Change-Id: Ie28a4db9fffb2d661592cf43f9316aa0824e4635