`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.

从 useResizeHandler 的实现开始，跟踪它当前如何订阅 window.resize。检查现有的调整大小处理相关测试，然后验证对已渲染 plot 元素的更改会触发调整大小，同时 window.resize 回退机制仍然有效。当可折叠布局的更改能够调整 plot 的大小，且无需手动调用 Plotly.Plots.resize() 时，即表示完成。