chore: pinning react and react-dom across every dependency

[erunion]

🧰 What's being changed?

We're running into some React hook hell when running the latest version of the explorer with tutorials integration in ReadMe with tutorials present on a project. We think it's because the versions of React that the explorer, ReadMe, the UI library, and @readme/syntax-highlighter aren't all the same so what I'm doing here is:

• Moving react and react-dom over to being dev dependencies, pinning them at the latest of the v16 series.
• Adding the same dependencies, at 16.x into being peerDependencies.
  • https://stackoverflow.com/questions/30451556/what-is-the-correct-way-of-adding-a-dependency-to-react-in-your-package-json-for
• Upgrading @readme/syntax-highlighter across the explorer and oas-to-snippet to 10.1.0 which does the same peerdep work chore: moving react and react-dom into being peerdeps syntax-highlighter#24
  • The legacy Markdown engine markdown-magic is being excluded from this because upgrading is changing span tags to div and inserting empty <code></code> elements where there weren't before. Since its the legacy engine, it should be fine? Hopefully that not being the same as everything else isn't the linchpin in all of this.
• Yakshaving every package file up a bit so they are all mostly identical.

I'm also extracting react and react-dom from being compiled into the explorer dist. Since the explorer is a reusable React component, it's always going to be used in an environment where React is present so we don't need to bloat up its bundle with another copy of React. The result is some wild drops in dist sizes:

• @readme/api-explorer: 5,199,205K to 4,644,622K. 11% reduction 👀
• @readme/api-logs: 33,273K to 25,863K
• @readme/variable: 15,266K to 7,919K

[rafegoldberg]

This is great. Changes look okay to me. Have you tried running an integration test against ReadMe proper?