GlyphGeometry

The `PangoGlyphGeometry` structure contains width and positioning information for a single glyph.

Note that width is not guaranteed to be the same as the glyph extents. Kerning and other positioning applied during shaping will affect both the width and the x_offset for the glyphs in the glyph string that results from shaping.

The information in this struct is intended for rendering the glyphs, as follows:

1. Assume the current point is (x, y)
2. Render the current glyph at (x + x_offset, y + y_offset),
3. Advance the current point to (x + width, y)
4. Render the next glyph