add pen style to symbol-json

[Kanahiro]

        symbol_layer_dict = {
            "size": convert_to_point(symbol_layer.size(), symbol_layer.sizeUnit()),
            "fill_color": symbol_layer.color().name(),
            "outline_color": symbol_layer.strokeColor().name(),
            "outline_width": 0
            if symbol_layer.strokeStyle() == Qt.PenStyle.NoPen
            else convert_to_point(
                symbol_layer.strokeWidth(), symbol_layer.strokeWidthUnit()
            ),
            "symbol_layer_type": "simple",
            "symbol_path": "",
            "level": symbol_layer.renderingPass(),
        }

It is bad to use zero-value even when PenStyle == NoPen, should set raw value and make another property outline_penstyle in this case.