Show appropriate date when date is part of grouped data on chart.

[onesimus-wiafe]

This PR addresses issue #2566. When the data is grouped and a date is part of the grouped data, the date values are then represented in epoch format. I couldn't figure out the exact source of the problem, and this solution addresses the problem. I included a function in the filter.ts file since all the plugins affected by this issue import the functions in filter.ts. I refine the date type values before the functions in filter.ts run. The tests included confirm this solution too.

Pull Request Checklist

• Description which clearly states what problems the PR solves.
• Description contains a link to the Github Issue, and any relevent
  Discussions, this PR applies to.
• Include new tests that fail without this PR but passes with it.
• Include any relevent Documentation changes related to this change.
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[texodus]

Thanks for the PR!

I suspect some parts of this PR are AI generated. We do not yet have an official project policy on this, but I'm not eager to review such code. If you're going to use these tools, please rigorously check for relevance, brevity and sanity before submitting - technically correct code is not enough. If this is not AI generated code - please do this anyway.

Regardless of the tooling, I would like some cleanup of this code before we merge it (see review comments).

[texodus]

Looks good!