Major new features:
- Array.prototype.{flat,flatMap} (Michael Ficarra,Brian Terlson,Mathias Bynens)
- Object.fromEntries (Darien Maillet Valentine)
Minor new features:
- String.prototype.{trimStart,trimEnd}(Sebastian Markbage)
- Symbol.prototype.description(Michael Ficarra)
- Optional catch binding (Michael Ficarra)
- Array.prototype.sort() is guaranteed to be stable (Mathias Bynens)
Changes that are mostly internal:
- Well-formed JSON.stringify (Richard Gibson)
- JSON superset(Richard Gibson)
- Function.prototype.toString revision (Michael Ficarra)
