wmr Rewrite node module handling (npm plugin)

This PR is a rewrite of the way we handle node modules and fetch them from the npm registry.

Add support for browser field in package.json
Unify development and production handling into a single plugin. Previously, we used a middleware during development and a rollup plugin for production
Prebundles dependencies to greatly reduce the number of requests. Previously, we'd fetch each file of an npm package individually.
Improve CommonJS handling by attempting to convert it to ESM. Note that CommonJS in general has severe limitations in an ESM world and can't be served correctly.
Auto installing of npm packages is moved to a CLI flag --autoInstall and is disabled by default. The auto install feature is contained in a separate plugin.
Support for monorepo setups. We'll now follow the node resolution algorithm and traverse upwards until we find a node_modules folder with the package we're looking for.
npm registry is not a global anymore and can be set from cli via --registry.
Get's rid of the setCwd hack 🎉
We didn't have any tests regarding the npm plugin, so this PR adds them. They make up the lion share of the changes.