~jaro/balkon

ref: 5d0bf7627c61fa5a70757ad5fe726b04eaa657c6 balkon/src/Data/Text/ParagraphLayout/Internal/Rich d---------
Implement calculation of safe paragraph width.
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.