Integrate BiDi reordering.

Represent lines with non-empty lists.

We can do this because we removed lines with zero size.

Remove lines with zero size.

These lines would otherwise affect line numbering.

Do not re-export through the Plain module.

Clarify comment about BiDi.

Fix style: white space in lambdas.

Fix style: white space around operators.

Fix style: white space in exports and imports.

Mark some lists as explicitly non-empty.

Separate module for the ParagraphLayout type.

Remove collapsible spaces at beginning of lines.

Allow empty lines when hard line breaking.

Support hard line breaks.

Document considerations for beginsText/endsText.

Properly use ICU locale identifiers.

Clarify spanLanguage and add basic ICU conversion.

Refactor line breaking.

Allow breaking at character bounds.

Use a single list of line breaking alternatives.

Implement trimming spaces at end of lines.