refactor: change plugin export from default to named

[spiltbeans]

Describing the problem

If you import the plugin as directed in the docs you may encounter a console error like:

import dts from "rollup-plugin-dts";

const config = [
  // …
  {
    input: "./my-input/index.d.ts",
    output: [{ file: "dist/my-library.d.ts", format: "es" }],
    plugins: [dts()],
  },
];

export default config;

[!] TypeError: dts is not a function

And you will be returned this if you log dts to the console:

{ default: [Function: plugin] }

This PR closes #247.

Describing the solution

This PR modifies the export of the plugin function as a named export called dts rather than export default.

Using named exports is less likely to encounter these inconsistent importing patterns in the future.

This StackOverflow thread provides multiple reasons why named exports are a favourable pattern for ES6. This response compiles relevant articles expanding on the issue.

Describing changes to the package

This PR would change the way this package is imported into projects. It will be a breaking change as importing will now be:

// new import
import { dts } from "rollup-plugin-dts";

// example usage
const config = [
  // …
  {
    input: "./my-input/index.d.ts",
    output: [{ file: "dist/my-library.d.ts", format: "es" }],
    plugins: [dts()],
  },
];

export default config;

[spiltbeans]

I've created an alternate PR in #275 to solve the same issue. They are different solutions and only one should be accepted.

[Swatinem]

Thanks for taking care of this. I would be curious about what part of the commonjs interop exactly is breaking this usecase here

[Swatinem]

Thanks again for looking into this! I will get a new release out during this week.