Build the React JSX runtime into a new WordPress script

[youknowriad]

Trac ticket: https://core.trac.wordpress.org/ticket/61324

Backports Gutenberg PR WordPress/gutenberg#61692

This PR adds the necessary webpack config to build the React JSX Runtime script and adds the script to WordPress. Without this, the next package update on Core will be blocked as the new packages are going to be using the new JSX Runtime.

For the moment though, you can test that the PR adds the react-jsx-runtime script to wp-includes/js/dist/vendor/react-jsx-runtime.js
Also if you load manually the react-jsx-runtime in WordPress, you'll see the ReactJSXRuntime global available in the console.

[github-actions]

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Props youknowriad.

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[youknowriad]

Also just like the backported PR, this moves react scripts we used in Core from the deprecated umd builds to CJS.

[github-actions]

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