`useResizeHandler` does not respond to container layout changes

Currently, useResizeHandler only responds to window.resize events.

This works when the browser viewport changes, but it does not cover layout changes that resize the plot without resizing the window.

For example, if a page contains a collapsible sidebar and a responsive plot in the same page, toggling the sidebar changes the space available to the plot, but no window.resize event is fired. The plot therefore keeps its previous size until Plotly.Plots.resize() is called manually.

Would it make sense for useResizeHandler to react to changes in the rendered plot element's size instead of only listening to window.resize?

One possible approach would be to use ResizeObserver when available, while keeping the existing window.resize listener as a fallback.

從 useResizeHandler 的實作開始，追蹤它目前如何訂閱 window.resize。檢查現有的調整大小處理相關測試，然後驗證對已渲染 plot 元素的變更會觸發調整大小，同時 window.resize 備援機制仍然有效。當可摺疊版面配置的變更能夠調整 plot 的大小，且不需要手動呼叫 Plotly.Plots.resize() 時，即表示完成。