Computes the logical and ink extents of this in device units.
This function just calls [method@Pango.LayoutLine.get_extents] followed by two [func@extents_to_pixels] calls, rounding
logical_rect such that the rounded rectangles fully contain the unrounded one (that is, passes them as first argument to [
rectangle used to store the extents of the glyph string as drawn
rectangle used to store the logical extents of the glyph string