feat: asset serving config for workers + assets (#6631)

* add asset config behaviour

move shared assets code to workers-shared/utils

add asset config to wrangler

add asset config to miniflare

add config binding to asset-worker

add asset config behaviour to AW (this is the big one)

make UW manually handle 404s

update assets-only fixture

fix drop-trailing-slash logic

html handling tests

* pr feedback

* fix tests and pr feedback 2

* changesets

---------

Co-authored-by: Samuel Macleod <smacleod@cloudflare.com>
Co-authored-by: Greg Brimble <gbrimble@cloudflare.com>

.changeset/green-pears-shake.md

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+---
+"wrangler": patch
+---
+
+Add config options 'html_handling' and 'not_found_handling' to experimental_asset field in wrangler.toml

.changeset/real-cheetahs-fry.md

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+---
+"@cloudflare/workers-shared": minor
+---
+
+Add asset config behaviour.
+
+Add `html_handling` (e.g. /index.html -> /) with options `"auto-trailing-slash" | "force-trailing-slash" | "drop-trailing-slash" | "none"` to Asset Worker.
+
+Add `not_found_handling` behaviour with options `"404-page" | "single-page-application" | "none"` to Asset Worker.

fixtures/asset-config/README.md

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+# Asset config fixture
+
+This is testing the asset worker in the workers-shared package. We cannot use the vitest integration directly in that package because it results in circular dependencies.
+
+Since it runs tests in a workerd context and doesn't depend on the host OS, this fixture only runs test on Linux to reduce wasted time in CI.

fixtures/asset-config/env.d.ts

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+declare module "cloudflare:test" {
+	// Controls the type of `import("cloudflare:test").env`
+	interface ProvidedEnv {
+		CONFIG: Record<string, string>;
+		ASSETS_MANIFEST: ArrayBuffer;
+		ASSETS_KV_NAMESPACE: KVNamespace;
+	}
+}