Gets the bbox of the bitmap centered around the glyph origin; so the bitmap width is ix1-ix0, height is iy1-iy0, and location to place
the bitmap top left is (leftSideBearing*scale,iy0).
(Note that the bitmap uses y-increases-down, but the shape uses
y-increases-up, so CodepointBitmapBox and CodepointBox are inverted.)
Gets the bbox of the bitmap centered around the glyph origin; so the bitmap width is ix1-ix0, height is iy1-iy0, and location to place the bitmap top left is (leftSideBearing*scale,iy0). (Note that the bitmap uses y-increases-down, but the shape uses y-increases-up, so CodepointBitmapBox and CodepointBox are inverted.)