Primitives: Implement `Cache` as `CacheStorage` interfaces

[Kikobeats]

The CacheStorage is holding all the

A CacheStorage object represents a name to cache map of its associated global object's:

self.caches // CacheStorage {}
self.caches instanceof CacheStorage // true

You can create a new Cache namespace there, and it will be an instance:

const cache = await caches.open('my_cache')
cache instanceof Cache // true

Additionally, CF Workers exposes a default single global cache object:

const cache = caches.default
cache instanceof Cache

This cache is a bit special: Since the spec actually doesn't provide any way to manipulate the cache that backs fetch(), if you put something into it, then fetch() will match that thing.