Enable the "development" [1] option for the `@babel/preset-react` preset
to enable more helpful warnings/errors from Preact in development
builds.

Note that the configuration added here _replaces_ rather than _augments_
the `@babel/preset-react` config for other builds, so other keys like
"createElement" also need to be specified in both places.

See https://babeljs.io/docs/en/babel-preset-react#development.