Add node emulation to `typehead serve`

# Description

Parcel bundler has "node integration" which mirrors what Webpack, Browserify, etc do. We wouldn't want to include this in the actual bundle, in case users are using Node.js or a platform we don't recognize, but we can do the following for `typescript serve`:

1) Prepend a `window.global = global;` since ESBuild doesn't do this by default.
2) Add the [esbuild-plugin-node-emulation](https://github.com/zfanta/esbuild-plugin-node-emulation) plugin.

Start at the `typehead serve` entry point and inspect how its esbuild configuration is assembled. Implement the two requested node-emulation steps, then verify that `serve` handles Node-style globals and modules without adding them to the regular bundle.

Written by the indexing model from the issue text.