Breaking changes to be made for MUI X v9:

• In Heatmap replace the default value of hideLegend prop by false
• Remove useAxisTooltip in favor of useAxesTooltip
• Remove the "All plugins" default value in ChartProApi (more info)
• Update useChartRootRef to accept HTMLElement | SVGElement instead of HTMLDivElement (more info)
• Consider using data attributes instead of class names with suffixes (e.g., .Mui-ChartsAxis[data-axis-id="xAxis"] instead of Mui-ChartsAxis-xAxis)
• Consider reducing built-in margins [charts] Remove/Reduce default margin values #17988
• Remove number series IDs [charts] Highlight doesn't work when series ID is a number #18415
• [charts] Refactor classes structure #18496
• Add "Chart" suffix in classes (e.g., MuiScatter -> MuiScatterChart)
• Remove ChartApi from ChartContainer/index.tsx
• Rework the notion of item highlight and axis highlight to have a single entry point
  • Reconsider the usage of axis.data for line and bar chart since they are the only one use use it
• Remove deprecated useAxisTooltip in favor of useAxesTooltip
• Avoid calculating extrema for unused series in getAxisExtremum. This is a breaking change because it will break the axis display example (source)