Gets the size field of a font description.
the size field for the font description in points or device units. You must call [method@Pango.FontDescription.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 [ method@Pango.FontDescription.get_set_fields] to find out if the field was explicitly set or not.