Fix recents order being reversed sometimes

Occasionally, the recents list items were reversed.  This is because
RecentsTaskList#getTasks returns the actual backing list which we were
reversing, so we solve this by making a new array list.

Bug: 131367388
Test: Do repro in bug, no longer gives reversed order
Change-Id: I825d284e4768c2b53fedf07480e99d195acfa6d6