feat: add geojson download feature

[JinIgarashi]

Description

I am adding a feature to download attributes as GeoJSON. However, there is still a bug which polygon geometries from queryRenderedFeatures split by tiles, the result cause the duplicated features in the same GeoJSON.

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Type of Pull Request

• Adding a feature
• Fixing a bug
• Maintaining documents
• Others ()

Verify the followings

• Have you referenced related issues in the repo if they are present (issues)?
• Code is up-to-date with the main branch
• No build errors after pnpm build
• No lint errors after pnpm lint
• Make sure all the existing features working well
• Updated documentation in the packages you modified in sites/svelte.water-gis.com folder and README.md of the package.

Changesets

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