Webidl support

[j-f1]

Progress on #21. Currently broken and I might start over

It seems like the 2 most important changes are:

• instanceof support (which is implemented hackily but is ultimiately necessary for properly type checking things)
  • I kinda want to re-implement this in a way that actually lets you provide the class object instead of pulling it off window.
• JSValue encoding/decoding to seamlessly pass in and return Swift values

Unrelated changes:

• instead of having type + 3 payload slots per object, have just type + two slots and interpret them as a combined double or two 32-bit ints depending on the type
  • this would cut down memory usage a bunch although I don‘t think it would really be a significant problem for a while
• instead of passing around kind, payload1, payload2, payload3, pass around a DataView into the memory object, offset to the right location
  • this makes it easier to pass around blobs of memory I guess, but not sure what the perf implications are

[kateinoigakukun]

@j-f1 Awesome progress! If you break this big change down into several small PRs, it would make it easy to review for me 🙏

[j-f1]

Will do! Closing in favor of #24 and future PRs