Add iterator helpers proposal types

[hurrymaplelad]

Missing/Incorrect APIs

Iterator.from() and Iterator.prototype.{*} from the tc39 stage 4 iterator-helpers-proposal.

Relevant documentation

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator
• https://github.com/tc39/proposal-iterator-helpers
• https://tc39.es/proposal-iterator-helpers
• TypeScript implementation
• Safari is the last major browser to implement. Support landed recently but hasn't shipped yet.