feat: Add directional resize buttons to split panel and drawers

[avinashbot]

Description

A lot of work still left to do:

• Confirm everything works well with widgetized app layout
• Figure out why importing this one internal component adds 30kB to the widget bundle
• Deal with the handles popping out on click (because of focus move)
• Clean up onDirectionClick handler implementation
• Provide tooltip text
• Add tests

Related links, issue #, if available: AWSUI-60241, AWSUI-60242

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?

---

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