~jaro/balkon

ref: 0975c99f8e8fc2f33c968daa8968444bb0c026c5 balkon/src/Data/Text/ParagraphLayout/Internal/Rich d---------
Refactor lineNumbers into a common module.
Integrate BiDi levels with spanToRuns algorithm.

Span/box boundaries no longer reset directionality.

BREAKING: Text with no strongly directional characters would
previously be treated as having no direction. It will now be
treated as having the direction defined in TextOptions.
This affects calculated positions.
Fix documentation: link to layoutRich.
Expose piecewise paragraph construction.
Consolidate tree types into one.
Add ancestor boxes to interface.
Implement Rich pagination.
Implement piecewise paragraph construction.
Add basic support for Rich layout.