feat: Add bubble series to cartesian chart component

[avinashbot]

Description

Adds a new "bubble" type for chart series, which accepts a z value in addition to x and y.

Related links, issue #, if available: AWSUI-61535

How has this been tested?

Modified existing unit tests that cover all series types to include bubble series. There's also a new dev page for the bubble chart, which (if I understand it correctly) is now screenshot-tested.

Also reviewed it with our accessibility specialists and visual designers. And of course, manually on some local browsers with VoiceOver.

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?

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[pan-kot]

@georgylobko, let's change getPointAccessibleDescription to include bubble size - or should we track it as a follow-up change?