Return copy of reposition bounds on drag start.

Drag start would return the instance of reposition bounds, rather than a
copy of it. This would then be altered by the calling method, changing
the coordinates to local space. This would interfere with the equality
check in onDragPositioningEnd, causing the veil to not be dismissed
correctly. This CL fixes that by copying the reposition bounds, similar
to the other methods.

Bug: 313500992
Test: Manual
Change-Id: I1757e936d1aa8f624e8db3e0fa4ceb87ef755b77