Update emotion support (MUI latest version) and add support for Node with ESM

[dgadelha]

• Updates Emotion imports to use @emotion/react instead of @emotion/core [reference]
• Add key to Emotion's createCache method, which is now required [reference]
• Add support for loading config from ssr.config.cjs, as Node.js with ESM (package.json's "type": "module" doesn't allow require of .js files [reference]
• Remove the dependency of urlsafe-base64, as it relies on Buffer API, which is not available in the browser

[dgadelha]

@saltyshiomix, somehow this is getting imported client-side and throws an Uncaught ReferenceError: process is not defined when rehydrating.

Locally, I've replaced this code with

const isProd = () => {
  return true;
};

but that doesn't seem to be the best option. I think maybe it is because the components (head, document) import the helpers.js, code that is ran client-side and fails.

I was only able to run this code with NODE_ENV=production, though. webpack-dev-server integration seems incomplete on 0.25.0-canary.2

EDIT: it seems that using import type { AlertColor } from "@mui/material"; and adding a prop color: AlertColor causes this behavior. I've removed this in my code and everything works fine now.

EDIT: fixed on last commit