Prototype pollution by Opal

[shishkin]

It seems that running Asciidoctor.js does pollute Javascript native object prototypes that leads to weird bugs. For example, this code adds a stub $id method to Array prototype so all arrays suddenly get it:

import asciidoctor from "@asciidoctor/core";

asciidoctor();

console.log([].$id);
// [Function: method_missing_stub] { '$$stub': true }
console.log(Array.prototype.$id);
// [Function: method_missing_stub] { '$$stub': true }

I discover a bug with this in ajv schema validator that runs into issues when it encounters an array of schemas with a present $id property, which it only expects to find on a single schema, not array.