Fix IndexOutOfBoundsException when calling dispatchProvideStructure()

dispatchProvideStructure() will get preorderedList by buildOrderedChildList().
buildOrderedChildList() returns mPreSortedChildren directly. During
the traversal, the mPreSortedChildren is changed by the
View#populateAccessibilityNodeInfoDrawingOrderInParent(). When one of
child traversal is done, the preorderedList is already changed, the
IndexOutOfBoundsException will occurr when trying to travese the next
child.

To fix it, try to make a copy not directly refer to mPreSortedChildren.
Bug: 185971133
Test: manual. App doesn't crash
Test: atest CtsAutoFillServiceTestCases
Change-Id: Ie077948dd45426c1204d153ca0a921c7c67351d8