chore: Split public and internal interface

[pan-kot]

Description

Same changes as in components repo: cloudscape-design/components#4703

How has this been tested?

• Dry-run to live (7927754436)

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[NathanZlion]

why is this one still importing LegendItem internal one?

chart-components/src/core/chart-api/chart-extra-legend.tsx

Line 6 in dc0b07f

import { LegendItem } from "../../internal/components/interfaces";

If we're moving it, shouldn't we move the whole thing instead of defining it in 2 places, is this intended for instance for LegendItem and the other chart props @pan-kot

Discussed internally