Issue #679: standardize custom tooltips via ToolTipGenerator on all series types

[timmolter]

Closes #679

What

Adds one standardized way to customize tooltip text on every chart type, replacing the ad-hoc per-chart-type approaches:

chart.getHeatMapSeries().setToolTipGenerator(
    dataPoint -> dataPoint.getLabel()
        + System.lineSeparator()
        + extraInfo[dataPoint.getDataPointIndex()]);

• New ToolTipGenerator functional interface (ChartDataPoint -> String), settable on the base Series class via a fluent setToolTipGenerator(...), so it works on XY, Category, Bubble, HeatMap, Box, OHLC, Radar, Pie, Dial, and HorizontalBar charts alike.
• The generator receives the series name, the data point's index within the series data (for looking up raw values / extra info in application data structures), the default formatted label, and screen geometry. Returning null falls back to the default label.
• Multi-line tooltips are supported: any label containing System.lineSeparator() is now painted multi-line (previously hardcoded to Box/OHLC stylers only — resolves an old TODO in ToolTips).

How

The generator is applied in exactly one place — ToolTipData.withSeries(series, index) in PlotInteractionData — so each PlotContent_* class only attaches series identity to its tooltips. That attachment already existed for XY, Category, Bubble, and HorizontalBar; this PR adds it to HeatMap, Box, OHLC, Radar, Pie, and Dial, which as a side benefit extends DataPointListener (#492) series/index reporting to those six chart types too. DataPointDispatcher reports the displayed (custom) label to listeners.

Deprecations (removal in 4.1.0)

• BubbleSeries.setCustomToolTips(boolean) / setToolTips(String[]) (Custom tooltips removed since 3.7.0 ? #545)
• RadarSeries.setTooltipOverrides(String[])

Both continue to work; a ToolTipGenerator takes precedence when both are set (documented and tested).

Tests / demo

• ToolTipGeneratorTest: six headless tests (no XChartPanel) covering label replacement, null-fallback, series identity/index correctness, the HeatMap case from the issue, and bubble precedence/backward compatibility.
• TestForIssue679 demo: HeatMap whose tooltips append per-cell application data, with tooltips enabled on the panel.

Full mvn test passes across all modules.

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