Padding the bounding rect was not enough, as we failed to shift the glyph
accordingly so that it would end up in the center of the bounding rect.
We also didn't take subpixel-positioning into account, which may shift the
position of the glyph too far to the right to be within the image size that
we reserve.
There are still cases where the glyphs seem clipped compared to the same
text rendered with CoreText, but that's because we end up shaping the
text slightly differently, resulting in different subpixel positions
than what CoreText chooses.
Change-Id: Icb88c829f86457b16bdecbc4c24b3f1c23448261
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
d0784ae43b