package.json has been updated to specify the minimum Node.js version

we require (>= 14.0.0), to avoid any confusing errors when building

static media.
The .babelrc file has been renamed to babel.config.json. This is the

modern filename, and some tools expect it, skipping .babelrc. We also

have the option to make this babel.config.js in the future, letting us

make the file more dynamic, if needed.
We also now define the dedent and django-gettext plugins, which

weren't previously enabled for Rollup-based JavaScript bundles. These

dependencies are provided by @beanbag/frontend-buildkit.

Removed node_modules and re-installed. Tested Review Board with the

new Djblets static media setup, and tested building a Djblets package.

Both worked.