chore: Replaced hardcoded css values with design tokens

[georgylobko]

Description

Replaced hardcoded border radiuses with Cloudscape design tokens, because they cause a regression in the 1T. No visual changes for VR.

Related links, issue #, if available: n/a

How has this been tested?

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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[georgylobko]

I also considered introducing a new design token for it, but using the existing popover token seems appropriate here

[jperals]

I think a specific design token is a better option. Although the popover border radius happens to have the same default value as this element, they are semantically distinct. Would everyone who customizes the popover border radius expect the chart empty state indicator to change as well? I'd say not necessarily.

Alternatively, maybe border-radius-card-embedded is acceptable, since this is similar to a card embedded in a chart.

[georgylobko]

$border-radius-card-embedded sounds like a good option, addressed. I wouldn’t introduce a new token for this element. Although the elements are semantically different, border radiuses should remain consistent across similar components in the design system