Gets the size field of a font description. See pango_font_description_set_size().
the size field for the font description in points or device units. You must call pango_font_description_get_size_is_absolute() to find out which is the case. Returns 0 if the size field has not previously been set or it has been set to 0 explicitly. Use pango_font_description_get_set_fields() to find out if the field was explicitly set or not.