Migrate to ES6 modules

Configure project to use ES6 modules to enable top-level await
capabilities. This change helps project to align well with modern JS
standards.

- Set `type` to `module` in `package.json`.
- Use import/export syntax in Cypress configuration files.
- Rename configurations files that do not support modules to use
  the `.cjs` extension:
  - `vue.config.js` to `vue.config.cjs` (vuejs/vue-cli#4477).
  - `babel.config.js` to `babel.config.cjs (babel/babel-loader#894)
  - `.eslintrc.js` to `.eslintrc.cjs` (eslint/eslint#13440,
    eslint/eslint#14137)
  - `postcss.config.js` to `postcss.config.cjs` (postcss/postcss#1771)
- Provide a workaround for Vue CLI & Mocha ES6 modules conflict in
  Vue configuration file (vuejs/vue-cli#7417).

postcss.config.cjs

@@ -0,0 +1,5 @@
+module.exports = {
+  plugins: {
+    autoprefixer: {},
+  },
+};