Package ent isn't maintained anymore, and using deprecated punycode #812

The ent package is still using the native punycode module which used to be bundled in Node.js < 21.

Starting in Node.js 21, this native module was deprecated (see official Node.js docs), and we now have to use the userland punycode.

And the following warning shows:

(node:1) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead. 

Since the latest version of ent is 9-years-old and the repository was removed from GitHub, I think we could replace ent with another heavily-used package, e.g. html-entities.

Environment details

• OS: macOS
• Node.js version: v21.7.3
• npm version: 10.5.0
• @google-cloud/common version: 5.0.1

Steps to reproduce

1. npm install @google-cloud/common
2. node --trace-deprecation -e "require('@google-cloud/common')" (on Node.js 21)

I'll make a PR.