Harmonizer

This harmonizer offers the ability to invoke a bundled version of the JavaScript library, [@apollo/federation], which composes multiple subgraphs into a supergraph.

The bundled version of the federation library that is included is a JavaScript Immediately Invoked Function Expression ([IIFE]) that is created by running the [Rollup.js] bundler on the @apollo/federation package.

When the [harmonize] function that this crate provides is called with a [ServiceList] (which is synonymous with the terminology and service list notion that exists within the JavaScript composition library), this crate uses [deno_core] to invoke the JavaScript within V8. This is ultimately accomplished using [rusty_v8]'s V8 bindings to V8.

While we intend for a future version of composition to be done natively within Rust, this allows us to provide a more stable transition using an already stable composition implementation while we work toward something else.