Enable the import/no-commonjs ESLint plugin rule

Given the amount of work put into removing `require`-calls from the code-base, let's ensure that new ones aren't accidentally added in the future.

Note that we still have a couple of files where `require` is being used, in particular:
 - The Node.js examples, however those will be updated to use `import` in PR 17081.
 - The Webpack examples, and related support files, however I unfortunately don't know enough about Webpack to be able to update those. (Hopefully users of that code will help out here, once version `4` is released.)
 - The `statcmp`-tool, since *some* of those `require`-calls cannot be converted to `import` without other code changes (and that file is only used during benchmarking).

Please find additional details at https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/no-commonjs.md

examples/webpack/main.js

@@ -1,6 +1,8 @@
 // Any copyright is dedicated to the Public Domain.
 // http://creativecommons.org/licenses/publicdomain/
 
+/* eslint-disable import/no-commonjs */
+
 // Hello world example for webpack.
 
 const pdfjsLib = require("pdfjs-dist");