Support BigInt in TypeScript runtime

[arendjr]

The TypeScript runtime currently has limited support for integers larger than 2^53-1. bigint types are used when passing u64 WASM primitives, but when they’re passed as part of a MessagePack-encoded structure, they will always use number, causing precision to be lost for larger numbers.

Recently a new PR for msgpack-js made it possible to use bigint with MessagePack as well: msgpack/msgpack-javascript#211

I think it makes sense for us to implement an opt-in option with a similar effect.

[sagacity]

Initial investigation indicates that the current way of dealing with large numbers in msgpack-javascript is by encoding them as strings, which isn't great. Let's (briefly) see if the PR mentioned by @arendjr will be merged. If not we can either choose to fork msgpack-javascript (or use the PR branch) or deal with large-numbers-as-strings on the Rust side of fp-bindgen.

[arendjr]

With a bit of luck, we might be able to include this in our own 3.0 release as well: msgpack/msgpack-javascript#211 (comment)

Might even be worthwhile to wait a bit for this (assuming it's not too long), as proper BigInt support would likely be a breaking change on our side as well.

[arendjr]

Unfortunately, their PR is still open, so we should go ahead with our 3.0 release without this.