custom data for hover label

[FabianLippoldZR]

Is your feature request related to a problem? Please describe.
Currently there is no way to attach custom data to plot points, e.g. for use in the hover label.

Describe the solution you'd like
I would like an easy way to use custom data for points in the label_formatter;

Describe alternatives you've considered

• A previous solution which would introduce a type parameter for the custom data was rejected Introduce type parameter for plot points egui#4719
• Putting all the drawn PlotPoint IDs with their custom data in a Arc<Mutex<HashMap>> to retrieve them later in the formatter is quite unwieldy and is nowhere close to performant enough

Additional context
Current use case is to show a "validity" field for each point on hover