Add type.d.ts declaration file for ESM usage

[jacobcassidy]

What?

Adds a declaration type.d.ts file to the @wordpress/prettier-config package so those using ESM imports don't get the warning: "Could not find a declaration file for module '@wordpress/prettier-config'".

Why?

Removes the annoying missing typescript declaration type warning by providing a declaration.

How?

Adds the following code (uses CommonJS by default, but allows ESM):

declare module '@wordpress/prettier-config' {
  const config: any;
  export = config;
}

Testing Instructions

1. Install @wordpress/script
2. Create an ESM prettier config file, such as prettier.config.mjs with the content import wpConfig from '@wordpress/prettier-config';
3. See the underline under the @ in the VSCode editor that shows the warning.
4. Add the index.d.ts file to the /node_modules/@wordpress/prettier-config/ of a working project.
5. Note that the missing declaration warning is now gone.

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Co-authored-by: jacobcassidy <[email protected]>

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