Removes esModuleInterop from tsd and adds star import for helmet

[fox1t]

Since this is a plugin consumed by final users if we use esModuleInterop: true (as was before this PR) we broke all builds for users that have it set to false. In fact esModuleInterop is always checked in the dependency tree by TS if skipLibCheck is not set to true: we need to be sure that our package works for both esModuleInterop configurations.

On the other hand, Helmet doesn't use the "infamous triplet" (it still uses the old export = syntax), so we need to import it using import * as helmet from 'helmet' as it is a more conservative approach.

Fixes: #94

This PR can't be merged before this fix is published: fastify/fastify#2555

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]

feel free to release

[gtolarc]

This patch seems to cause a problem with the esModuleInterop=true setting. Is there a solution?

[gtolarc]

I think it would be better to revert. import * as helmet from "helmet"; -> import helmet from "helmet";

[mcollina]

Can you send a PR?

[fox1t]

Unfortunately, we can't just revert this because we will break the other case again. Can you create a repro repository so we can investigate further into this?

I can't understand why this worked both during my local testing and in the CI/CD.

I'll double-check the last import that is left to test:import helmet = require('helmet')

[fox1t]

@mcollina here the fix: #96

I think that from now on if we need external types that are defined as export = (so CommonJS namespace) we should enforce the use of import = require. I'll check that this guideline is followed. In addition, as I propose in that PR, we need to add more tests to catch these scenarios.