misc: add module types declaration

[Dumeng]

Summary

Feature: Add module declaration file for better typescript support.
The types is generated using below command.
npx /lighthouse-core/index.js --declaration --allowJs --emitDeclarationOnly --outDir types

For current version, if we create a TS project and attempt to import lighthouse, it will throw an error about missing module types declararion.

TS doc for package.json types field
TS doc for generating .d.ts files from .js files

Related Issues/PRs

#1773

[brendankenny]

Have you tried using these types? I don't believe they'll work because they reference global lighthouse types (under the global.LH namespace) that won't be defined for users of this file.

For #1773 to really be solved, I think the exported types will need to be written manually, the global LH types will have to eliminated, or some fancy api-extractor magic will need to happen (or some combo of the three).

[Dumeng]

You are right. I refer the global types in my test file, so it looked fine for me.

I have commit an updated version.

Because the project already has type files for most of source code. So this PR only generated the types for the main index.js. I think it's a good start. And now I added manually type declarations to the modified the auto-generated file. Maybe it's not the final version, but I hope it will cover the most common scenario.

[connorjclark]

We can't accept a solution that isn't 100% done and automated, and we can't prioritize working on this at the moment.