[FIX] layout/Splitter: Correctly calculate content sizes

After an orientation change the Splitter bars were incorrectly sized
if the Splitter was not rerendered. This fix changes the order of
calculation and resets the Splitter bars before using them to calculate
the available height/width.

Change-Id: I17a84c6799f60f191b33de1291a8b9cfe4eb7bd3
Merge "[FIX] layout/Splitter: Correctly calculate content sizes"