~jaro/balkon

ref: ca37c6e309c0e50ea21dbc823c34b4f21c38c977 balkon/src/Data/Text/ParagraphLayout/Internal d---------
Expose ParagraphConstruction.
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.