Store default level in BiDiLevels.
This will be required for handling empty text sequences.
Internally mark hard line breaks.
Internally allow splitting texts at endpoints.
This is required in order to preserve a hard line break at the end of
the input.
Simplify code since run direction is always known.
Improve BiDi handling of numbers and neutrals.
Add tests for mixed text direction.
Test spanToRuns independently for scripts/directions.
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.
Convert legacy span directions into levels.
Move BiDi Level to separate module.
Add expected run lengths to test data.
Deduplicate emptyFont in RunSpec.
Generalise text from SpanData for other tests.
Add Arabic examples to spanToRuns tests.
Consolidate tree types into one.
Implement finding box edges.
Add required textDirection to TextOptions.
Use ResolvedBox when flattening trees.
Implement BiDi resolved level reordering.