[Feature Request] Add findLastIndex function to std/collections

[kawarimidoll]

Array has finding functions, find() and findIndex().
find() returns the element, and findIndex() returns the index.

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/findindex

Now, we have findLast() in std/collections, this returns the element.

• https://deno.land/std/collections/find_last.ts

So, how about add findLastIndex() ?
It is almost same as findLast(), but returns the index of the last found element.

import { Predicate } from "./types.ts";

export function findLastIndex<T>(
  array: Array<T>,
  predicate: Predicate<T>,
): number {
  for (let i = array.length - 1; i >= 0; i -= 1) {
    const element = array[i];

    if (predicate(element)) {
      return i;
    }
  }

  return -1;
}

[kt3k]

Because we already have findLast in std/collections, this proposal makes sense to me.

This can be implemented in V8 in some future https://github.com/tc39/proposal-array-find-from-last https://chromium-review.googlesource.com/c/v8/v8/+/3037160 . If that happens, then let's deprecate it.