Add paragraphLines to Rich ParagraphLayout.

BREAKING: The paragraphLines field of ParagraphLayout must be preserved
for pagination.

BREAKING: The width of a rich text ParagraphLayout will now remain
unchanged after pagination.

BREAKING: Empty space at the top of the first line and at the bottom
of the last line in a ParagraphLayout will now be preserved.

Use more specific name for the LineHeight typeclass.

Implement calculation of safe paragraph width.

Refactor lineNumbers into a common module.

Add ancestor boxes to interface.

Implement Rich pagination.

Add basic support for Rich layout.