Add BigInt bindings

[tom-sherman]

Relates to #4677.

This is my first ever ocaml code, would appreciate if someone could help getting the PR ready to be merged - or just outline what I need to do. Thanks!

[cannorin]

ts2ocaml would greatly benefit from having bigint defined & supported in rescript.

I'm willing to help this if you need a hand.

[cristianoc]

How about reviving this? First by rebasing on master, then revisiting any open questions left.

[DZakh]

I've created a PR in which added the BigInt module https://github.com/rescript-lang/rescript-compiler/pull/5531. I think it should be good enough as the first iteration.

[bobzhang]

I am thinking we may provide native bigint in the long term

[cristianoc]

ts2ocaml would greatly benefit from having bigint defined & supported in rescript.

I'm willing to help this if you need a hand.

What's required specifically for ts2ocaml? Frankly speaking, that project has great potential and I'm simply interested in removing obstacles in the way to see what comes out of it.

[cannorin]

#5539 solved the core problem, as ts2ocaml now don't have to define bigint on our own and just use BigInt.t.

It would certainly help if we can have a proper bigint binding, but it doesn't need to be available as soon as possible 🙂

[tom-sherman]

Going to close this PR now that we have #5539. I wanted to add these so that we can have a shared bigint type across third party code, the bindings are not so important to me.