Fix an offset error.

[rect.x(), rect.y()] actually represent the top-left corner of the
available space. So in this case we should not adjust x with the width of
the item rect or the whole layout will shift to the left.
Fix a reduce error

When a chunk is placed at the top-left or top-right, we should not adjust
its y position when an item is added, but only reduce its height.
Fix position of items in the RIGHT_BOTTOM_TOP case.
Update the generated files.