Allow ES2020 BigInt values to be passed to operations taking integers.

[ExE-Boss]

ES2020 adds the BigInt type, which allows for integers outside the ‑253...253 ‑ 1 to be represented in JavaScript code.

This makes it possible to handle the full range of long long and unsigned long long values in JavaScript.

[bzbarsky]

Please see #525

[bzbarsky]

And in particular, the decision there was that BigInt will be a separate type not passable to operations taking integers, for consistency with ES.

I assume you meant long long and unsigned long long, by the way, since the full range of long and unsigned long is not a problem in the ES bindings.

[ExE-Boss]

Yeah, I keep mistakenly thinking of the Java long type, which is an i64, whereas WebIDL uses the C long, which is an i32.

I suggest we rename them to remove this confusion: #843.

[annevk]

Let's dupe this into that PR.