FigureWidget `shapes` property is empty, even when it's populated in `_props`

When using FigureWidget, the shapes property does not update properly.

Here is an example:

fig = go.Figure()
fig.update_layout(
    modebar={"add": ["drawline", "drawclosedpath", "eraseshape"]},
)
widget = go.FigureWidget(fig)
widget.show()

When I draw a shape, widget.layout["shapes"] remains empty. On the other hand, widget.layout._props["shapes"] is populated correctly.

This is using Plotly 6.2.0.

使用所示的 FigureWidget 範例重現問題，然後追蹤繪製形狀後 widget.layout["shapes"] 和 widget.layout._props["shapes"] 如何被填入。比較公開屬性與內部 props 的行為，並在公開 shapes 屬性反映出所繪製的形狀後確認完成。