Add content rect to Fragment.

Test preservation of lines with boxes.

Test boxes with no text or only a space.

Allow trimmed whitespace to generate empty fragments.

BREAKING: Output may now contain more fragments with zero glyphs,
representing runs of whitespace that was trimmed away. These runs may
also start a box at the end of a line, instead of the beginning of the
next line.

BREAKING: Trimmed whitespace now affects line height.

Test with AlignStart by default.

Test centred paragraph.

Allow paragraphRect without point 0,0.

Test right-aligned paragraph.

Test handling of empty lines.

Make RTL text overflow the left paragraph edge.

This behaviour is consistent with CSS Text Module Level 3.

BREAKING: Previously, all text would overflow the right paragraph edge,
regardless of text direction.

Test mixed line height.

Test ultra narrow Arabic text.

Test shaping across intra-word breaks.

Improve BiDi handling of numbers and neutrals.

Autodetect text direction for legacy interface.

Test with only directionally neutral characters.

Test mirrored neutral characters.

Add shaped runs output for bidirectional text.

Add tests for mixed text direction.

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.