chore(docs): fix console warnings, codesandbox builds

[evwilkin]

Closes #11

This PR:

• Updates example exports to be named exports to avoid console warnings (export const Example... vs. const Example .... export default Example)
  • These errors are thrown by our code in mdx-ast-to-mdx-hast.js which throws an error when the name of an exported example cannot be easily parsed.
  • See codesandbox.js for the supported example export naming conventions.
• Fixes Codesandbox builds for examples as the default example exports were breaking those examples - named exports fixes this.
• Updates the relative import of the realTestData.js file across examples to an absolute import path to fix an issue of the relative import breaking the Codesandbox examples.

[nicolethoen]

Ran it locally and it all looks good! :)

[github-actions]

🎉 This PR is included in version 6.1.0-prerelease.1 🎉

The release is available on:

• GitHub release
• npm package (@prerelease dist-tag)

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