The whitespace-normalization loop in prepare_text() called
StringBuilder::append() on each code point, which resolves to the
`char` overload and truncates non-ASCII characters. measureText("ó")
therefore returned a width of 0, despite fillText painting the glyph.
Use append_code_point() instead, and add a regression test for both
precomposed and decomposed accented text.
4f54b16315