Add MapCursorEvent component

[PaulioRandall]

What does this change?

1. Adds <MapCursorEvent> component that provides a Svelte interface to the MapCursor functionality.
2. Adds test data & updates <Map> and <MapCursorEvent> stories.

Why?

It's easier and less verbose to add events via a component than within JavaScript code.

How is it tested?

Storybook + live applications.

How is it documented?

Storybook

Are light and dark themes considered?

N/A

Is it complete?

• [x] Have you included changeset file?
• [x] If this adds a new component, is it exported via index.js?