Docs: Remove react-dom@18 warning in docs

[tmeasday]

Closes #20729

What I did

As planned:

• Create a package @storybook/react-dom-shim with two entry points
  • the first one (. => /dist/react-16) uses react-dom@17's code path
  • the second (/dist/react-18) uses react-dom@18's.
• In @storybook/react and @storybook/addon-docs depend on the above, import the former and use in the place of react-dom.
• Additionally, add an alias in both packages (or perhaps a preset dependency on the shim package which adds an alias), which does something along the lines of:

import { readJSON } from 'fs-extra';

export const webpackFinal: StorybookConfig['webpackFinal'] = async (config) => {
  const reactDomPkg = await readJSON(require.resolve('react-dom/package.json'));
  const isReact18 = reactDomPkg?.version?.startsWith('18') || reactDomPkg?.version?.startsWith('0.0.0');

  if (!isReact18) return config;

  return {
    ...config,
    resolve: {
       ...config.resolve,
       alias: {
         '@storybook/react-dom-shim': '@storybook/react-dom-shim/react-18'
       }
    }
  };
};

And similar for Vite.

How to test

Render story + docs and check for react warning (and that it works) in:

1. react 17 project
2. react 18 project
3. react 18 project with legacyRootApi = true
4. non react project

(all of the above in WP + vite)

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[IanVS]

This seems like a much less hacky way of handling react version support. 👏

I had a few comments, and a concern about Vite dealing with absolute paths, but I don't have a chance to test it right now, so maybe it's fine.

[valentinpalkovic]

I love the changes <3

[ndelangen]

code LGTM