Rename optionalChaining to Object.get and introduce Object.set

[medikoo]

Reasoning:

• Object.get is simpler and better name
• Current implementation cover purely properties resolution, while real ECMAScript optional chaining is also about possible function invocations
• It'll be close to lodash's _.get, therefore easier to migrate for users that rely on lodash
• Having that we can introduce an Object.set, a conditional resolver that will create eventual objects on the way.

---

To be introduced in ext@1