~jaro/balkon

ref: 8b8b095a2d7cc321b520b3d3dc707f3f0501d2e3 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.