Stage 3: Array find from last

Proposal for the .findLast() and .findLastIndex() methods on array and typed array.

Motivation
Finding an element in an array is a very common programming pattern.
It can improve performance by avoiding obvious overhead and improve the constant factors in the time complexity. It can be useful in some performance-sensitive scenarios. eg: React render function.

Core Feature
Adds Array.prototype.findLast and Array.prototype.findLastIndex.

This would behave the same as Array.prototype.find and Array.prototype.findIndex but would iterate from the last to the first.

Code examples

const array = [{ value: 1 }, { value: 2 }, { value: 3 }, { value: 4 }];

array.find(n => n.value % 2 === 1); // { value: 1 }
array.findIndex(n => n.value % 2 === 1); // 0

// ======== Before the proposal =========== 

// find
[...array].reverse().find(n => n.value % 2 === 1); // { value: 3 }

// findIndex
array.length - 1 - [...array].reverse().findIndex(n => n.value % 2 === 1); // 2
array.length - 1 - [...array].reverse().findIndex(n => n.value === 42); // should be -1, but 4

// ======== In the proposal =========== 

// find
array.findLast(n => n.value % 2 === 1); // { value: 3 }

// findIndex
array.findLastIndex(n => n.value % 2 === 1); // 2
array.findLastIndex(n => n.value === 42); // -1

Polyfills
https://github.com/zloirock/core-js#array-find-from-last