[example] Add preact-next example

[oliviertassinari]

Because bundle size matter. Closes #14798. The Preact integration might not be perfect yet. This example will be a playground for us.

• react-dom 33 kB gzipped: https://bundlephobia.com/result?p=react-dom
• preact 4 kB gzipped: https://bundlephobia.com/result?p=preact@next

This change creates precedence for us in the support of Preact. Preact market share is small: https://www.rank2traffic.com/preactjs.com. However, they seem to take React compatibility very seriously: https://github.com/developit/preact/releases/tag/10.0.0-beta.0. It's an awesome alternative for people who wish to minimize the bundle size (-25kB gzipped). I hope it won't require any major effort. Maybe it will get traction 🤷‍♂️? No matter what, it helps with the "bloat" fear.

[mui-pr-bot]

No bundle size changes comparing 522c8f7...982bae1

Generated by 🚫 dangerJS against 982bae1

[yuqianma]

It seems like you install the es-lint things globally?
I cannot run the example with a simple npm install. Too many packages are missing.
Finally get it run after commenting the "First, run the linter" section in webpack.config.js

[yuqianma]

BTW, the TextField with preact is broken now.
Have no idea what's the problem so far...

[yuqianma]

Find a workaround:

const TextField = (props) => {
  const [value, set] = useState(props.value);
  return <OTextField
    {...props}
    value={value}
    onChange={e => set(e.target.value)}
  />
}

[oliviertassinari]

@yuqianma Do you know why it makes a difference?

[yuqianma]

@oliviertassinari Not really. I first guess it's related to this PR in 10.0.0-beta.1. But I tried to install beta.0. It's also broken.
Other possible is ref?

Since it's a bit complex to dig in the problem and I find the workaround. I want to get mine things done first.

Raise a issue with codesandbox at preact
preactjs/preact#1759