Defer importing polyfills (esp. node-fetch)

[tnzk]

Background

Parcel client cannot be bundled with ViteJS since it fails to pre-bundle a package with dependency to node-specific module. Parcel client has direct dependency to node-fetch, which in turn depends on a bunch of node-specific features, to polyfill fetch.

Solution

• Defer importing polyfills until just before it is actually used, so Vite won't try to bundle node-specific packages.
• Use ky-universal to polyfill instead
• Update Jest config to support ESM and top-level await, which mentioned by code comment in polyfill.ts as the blocker to use ky-universal directly.

My Svelte app works fine with these changes and setting vite.optimizeDeps.exclude to ['node-fetch']. I suppose Vue apps may be the same.

It passes all unit tests that passes at main on my end, but not really confident if this works in node as well.