[FEATURE]: Add modebar button to download figure JSON #7917

Hi Plotly team,
Could Plotly add a built-in modebar button to download the current figure as Plotly JSON?

Use case: in scientific visualizations, users often generate a plot in a web app, then want to customize it further by editing the underlying figure definition. Vega users can inspect/export a Vega spec and modify it directly; it would be useful to have a similar path for Plotly figures.

Ideally the button would export the current figure as JSON containing data, layout, and optionally config.
This can be implemented today with a custom modebar button, but built-in support would standardize the behavior and avoid every project reimplementing it.

Thanks for considering it.