Generate types for `src/service-worker.js`

[kwangure]

Describe the problem

At present you need to add types for the service worker to clue TypeScript in about the WebWorker scope and set self to ServiceWorkerGlobalScope.

Describe the proposed solution

SvelteKit should generate types into the types folder.

Alternatives considered

Writing my own types. It typically involves adding triple-slash directives in my src/service-worker.js.

/// <reference no-default-lib="true"/>
/// <reference lib="esnext" />
/// <reference lib="webworker" />

self.addEventListener('install', (event) => {
	/** @type {ExtendableEvent} */ (event).SpecialServiceWorkerStuff

And creating src/service-worker.d.ts

declare const self: ServiceWorkerGlobalScope;

Importance

nice to have

Additional Information

TS Context: https://github.com/microsoft/TypeScript/issues/14877.