ReadonlyheightTotal height in world units — lineCount · size, measuring from the first
line's cell top to the last line's cell bottom (the two are the same
because a cell is exactly one lineHeight tall).
ReadonlylineNumber of lines: one more than the \n count, or 0 for the empty string.
Zero rather than one for "" so that an empty label has zero height and
occupies no space in a layout — a caller that reserves a line for empty text
wants Math.max(1, lineCount), which is explicit at the point that wants it
(decision, WP-3a.4).
ReadonlyquadsOne quad per drawn glyph, in reading order, line by line.
Blank glyphs — the space, and anything else a font marks
BitmapGlyph.blank — advance the pen but
emit no quad: a fully transparent rectangle costs a draw call and a blend
and contributes nothing. So quads.length is not the string's length, and
a caller mapping quads back to characters must track that itself.
ReadonlywidthWidth of the widest line in world units; 0 for text with no glyphs.
What layoutText produces.