Provide a prebuilt iOS OCaml cross compiler for at least one architecture

[wokalski]

Adding iOS should be very simple. The main thing that's blocking us is Esy tooling with cross compilation. What we could do though is simply compiling a cross compiler for iOS that would be distributed as a binary and add esy.json to its repo. Is it possible?

Having at least one cross compiler would allow us to develop the platform while we're waiting for proper cross compilation support in esy.

Also, if we figure this out, we can do the same with Android.

[rauanmayemir]

The cross-compiler itself won't give us much as we'll need build configs to correctly compile target dependencies and target dependencies' target dependencies.

Hopefully, esy/esy#732 will be merged by the end of the week and we could start adapting our bindings for iOS. I already have a feature branch for esy that gives us the cross-compiler for dune, we'll be able to experiment with it soon.