Usage of `BigInt.prototype.toString()`

[claybiockiller]

Currently, only Number.prototype.toString() is used in the optimizer, but it has a disadvantage: it would be limited by MAX_SAFE_INTEGER. BigInt.prototype.toString() is not affected by that. To get number in BigInt type, you can just call "return "+number written in string+"n" in Function().

[fasttime]

Thanks! This should indeed work in all new browsers.