Adds the "infamous triplet" and exports default and names exports in TypeScript types

[fox1t]

This PR is the result of the ongoing talks about supporting all import contexts for the fastify ecosystem. We can use it as a case study for other core plugins.

What is important to note is that it is not enough to add this code only at JS, since the exported typings need to be updated too.

• Adds the "infamous triplet" in module.exports
• Replaces namespace export with "infamous triplet" in TypeScript typings
• Adds test for all TS imports
• Adds test for ESM context

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

lgtm

[mcollina]

lgtm