Reexport TypeScript types

[ddbeck]

This fixes two issues with the types we use in web-features:

• Types aren't exported, which makes it inconvenient to write code the conforms to web-features's types
• The types rely on a specific tsconfig, which fails type checking in some configurations.

Fixes #1980. See also Jym77/web-features-ts-esm, which was essential for fixing these issues.

If you want to try this version of the package, check out this branch and follow steps along these lines.

npm install
npm run build
cd packages/web-features
npm pack --pack-destination=$SOME_PACKAGE_WORKSPACE
cd $SOME_PACKAGE_WORKSPACE
npm install web-features-3.*.tgz
# do something with the package, e.g., npm test