✨ Integrate Spyglass web API

[SPGoding]

• Changed to download resources from api.spyglassmc.com instead of from GitHub.
• Replaced the old Downloader with something using the Cache API and fetch(). Implemented a very simple shim of the Cache API in NodeJsExternals.ts.

Fixes #1734 and resolves #1480.

[misode]

Testing this branch locally, a lot (but not all) mcdoc symbols are borked.

Looking at the warning paths, maybe the stripLevel is incorrect now?

[misode]

I experienced a corrupt vanilla-data cache once during unstable internet, but I can't really reproduce this.

I also experienced an error once that said versions.sort is not a function (in resolveConfiguredVersion), this would indicate that versions was not underfined, but also not a list, which seems really strange. Writing this I realized this might've been an { "message": "..." }, so maybe fetcher.ts is not handling 4xx and 5xx responses correctly