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.
Test mixed line height with varied alignment.
Add content rect to Fragment.
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.