Adapter bundle

[Rich-Harris]

Mostly just playing around for now, but this is intended to solve the perennial problem of dependencies behaving weirdly, by allowing adapters to determine what gets bundled.

For example, adapter-node doesn't need to bundle anything, but an adapter for a serverless platform might. Right now I'm trying to get esbuild to bundle everything inside the Vercel adapter, but it's possible that this belongs in an adapter util.

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[Rich-Harris]

This is a little tricky to test without actually releasing new adapter versions and trying to deploy stuff with them, so I'm going to do exactly that