~jaro/balkon

ref: 0f7131a5849c78c78573ed1abc34893b3ad1f64d balkon/src/Data/Text/ParagraphLayout/Internal d---------
Add required textDirection to TextOptions.
Link ResolvedSpan to boxes.
Use ResolvedBox when flattening trees.
Define ResolvedBox.
Improve code readability with type alias.
Separate WithSpan for sharing with other modules.
Deduplicate pagination code.
Implement Rich pagination.
Qualify Plain pagination.
Make paginateAll generic.
Implement piecewise paragraph construction.
Refactor pagination to allow rich layout.
Convert plain layout to a wrapper over rich layout.
Add basic support for Rich layout.
Embed TextOptions in ResolvedSpan.

SpanOptions are relegated to the legacy Plain interface, and
TextOptions are now being used internally.
Define tree for structuring paragraph content.
Define BoxOptions and TextOptions for formatting.

Differentiating the two record types reflects the fact that the root
inline box cannot be styled but its text contents can.
Separate interface-independent layout algorithm.
Separate interface-independent constants.
Add user data to spans.
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