Hovering over legend items doesn't work anymore

[vaadin-bot]

Originally by HermanBovens

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As can be seen also on the Vaadin Charts demo site, when hovering over legend items the series is not emphasized anymore as it used to be and as is also the behaviour shown at the HighCharts demo site.

What is expected is that e.g. for a pie chart the corresponding slice is highlighted. Other chart types have their own behaviour in HighCharts (e.g. making the line bold in a line chart), and previously also in Vaadin Charts.

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Imported from https://dev.vaadin.com/ issue #15505

[anasmi]

Still valid in 4.2.0 (Vaadin 8)