feat(WebAssembly): Make WebAssembly.Global generic

[ExE-Boss]

This makes WebAssembly.Global generic to better match the runtime behaviour:

• https://webassembly.github.io/spec/js-api/#globals

---

Q: Should I change this to use something more like:

declare namespace WebAssembly {
	class Global<T extends ValueType = ValueType> {
		constructor(descriptor: GlobalDescriptor<T>, v?: ValueTypeMap[T]);
		value: ValueTypeMap[T];
		valueOf(): ValueTypeMap[T];
	}

	type ValueType = keyof ValueTypeMap;
	interface ValueTypeMap {
		i32: number;
		i64: bigint;
		f32: number;
		f64: number;
	}
}

[sandersn]

The types look like an improvement to me. @saschanaz would it be better to fix this upstream somewhere instead of overriding it here? If not I think this would be appropriate here.

[saschanaz]

The IDL syntax does not support this kind of generics, so I think we need to override them. Looks good to me, feel free to merge 👍