Expose caches to Cloudflare adapter through Platform

[venashial]

This PR exposes Cloudflare's Worker Cache API as caches in the platform object. This allows hooks to do elaborate caching, for example, I use the Cache API to cache certain pages based on request cookies.

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Latest commit: 5ca08b5

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@sveltejs/adapter-cloudflare	Minor

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[benmccann]

lgtm, but I'm not the most familiar with Cloudflare, so will leave this for others to review as well

[benmccann]

I wonder if we should show these in alphabetical order?

[venashial]

I put caches at the bottom because it is the least likely to be used.

[Rich-Harris]

thank you!