[charts] Fix Scatter series highlight when id is a number

[JCQuintas]

Issue was due to Object.keys() returning an array of strings even if the keys are numbers.

This fix stores the seriesId as a property inside the series object to avoid the issue mentioned above.

Fixes #12603

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[mui-bot]

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[alexfauquette]

The solution looks good.

While looking at your solution, I was thinking that maybe I made a mistake by mixing the series and the delaunay in the same ref.

What do you think about splitting them into two distinct refs. One for the series and one for the delaunay, such that the isSeries would not be necessary?

[JCQuintas]

The solution looks good.

While looking at your solution, I was thinking that maybe I made a mistake by mixing the series and the delaunay in the same ref.

What do you think about splitting them into two distinct refs. One for the series and one for the delaunay, such that the isSeries would not be necessary?

Makes sense, I thought about that, but imagined there was a reason for it being this way. And since I still don't have a lot of context on the repo I decided to leave it as I had found it. 😅

[alexfauquette]

Nice code improvement 👍