Add type declarations to the packages

[Lehoczky]

Hi there 👋

It is now possible (and very convenient) to use JSdoc type annotations in the prettier config file to get autocomplete suggestions:

// prettier.config.mjs,

/**
 * @type {import("prettier").Config}
 */
const config = {
  trailingComma: "es5",
  tabWidth: 4,
};

export default config;

It would be great if this plugin also provided its own type declarations, because users could do something like this then:

/**
 * @type {import("prettier").Config & import('prettier-plugin-astro').PluginOptions}
 */
const config = {
  ...,
  astroAllowShorthand: true // autocomplete works
}; 

As an example, prettier-plugin-tailwindcss already does this:

/** @type {import("prettier").Options & import('prettier-plugin-tailwindcss').PluginOptions} */
export default {
  ...,
  plugins: ["prettier-plugin-tailwindcss"],
  tailwindConfig: "./tailwind.config.ts",
}