Premium Analytics: port the Visitors by location widget

[nerrad]

Fixes: WOOA7S-1487

Proposed changes

• Ports the Visitors by location widget into the Premium Analytics customizable dashboard.
• Registers the jpa/visitors-by-location widget and renders the shared visitors by location widget inside WidgetRoot using dashboard-level report params.
• Adds standalone Default / WithComparison Storybook stories plus a WidgetDashboardWithWidget dashboard story for the widget.
• Keeps the final trunk diff scoped to the Visitors by location widget package, its Storybook story, and changelog entries.

Storybook screenshot

Captured from the local Storybook widget dashboard story.

Related product discussion/links

• WOOA7S-1487; parent WOOA7S-1457.

Does this pull request change what data or activity we track or use?

No.

Testing instructions

• pnpm run lint-file projects/packages/premium-analytics/widgets/visitors-by-location/package.json projects/packages/premium-analytics/widgets/visitors-by-location/render.tsx projects/packages/premium-analytics/widgets/visitors-by-location/stories/visitors-by-location-widget.stories.tsx projects/packages/premium-analytics/widgets/visitors-by-location/widget.ts
• pnpm --filter @automattic/jetpack-premium-analytics typecheck
• pnpm --filter @automattic/jetpack-premium-analytics build
• pnpm --filter @automattic/jetpack-storybook storybook:build
• Verified the Storybook story packages-premium-analytics-widgets-visitorsbylocation--widget-dashboard-with-widget against the built Storybook iframe: title rendered, country data rendered, no NaN/undefined, and no unexpected widget console errors.

[github-actions]

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Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

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