~jaro/balkon

ref: 96f9cb996ba9947513bbfd6a99afc5d7903754db balkon/src/Data/Text/ParagraphLayout/Internal d---------
Hide Rect union from public interface.

The function behaves in a specific way that should not be relied on by
other modules.
Use internal library to hide non-public modules.
Move non-public modules into Internal namespace.