Implement findLast & findLastIndex on TypedArray's

[dirkdev98]

ECMASCript feature

Implement missing %TypedArray%.prototype.findLast ( predicate [ , thisArg ] ) and Array.prototype.findLastIndex ( predicate [ , thisArg ] ) features.

Implementing these should fix most of the remaining test262 tests with feature array-find-from-last.

Example code

// From test/built-ins/TypedArray/prototype/findLastIndex/return-index-predicate-result-is-true.js

var sample = new Int32Array([39, 3, 9]);
var called = 0;

var result = sample.findLastIndex(function() {
  called++;
  return true;
});

assert.sameValue(result, 2, "returned true on sample[2]");
assert.sameValue(called, 1, "predicate was called once");

[dirkdev98]

I want to implement this!

At some point the spec changed to use FindViaPredicate ( O, len, direction, predicate, thisArg ) for Array.prototype.find, Array.prototype.findLast, %TypedArray%.prototype.findLast, et al. Do we want to refactor the existing implementations to use this?

If so, where would be a good place to add this? Under built-ins/array/mod.rs as a pub(crate) fn find_via_predicate? I don't have any experience with Rust modules yet, so a bit unsure what the way to go would be.

[HalidOdat]

At some point the spec changed to use FindViaPredicate ( O, len, direction, predicate, thisArg ) for Array.prototype.find, Array.prototype.findLast, %TypedArray%.prototype.findLast, et al. Do we want to refactor the existing implementations to use this?

Yes, that would be optimal, This could be done In a separate PR.

If so, where would be a good place to add this? Under built-ins/array/mod.rs as a pub(crate) fn find_via_predicate? I don't have any experience with Rust modules yet, so a bit unsure what the way to go would be.

Yes, that's a good place :) , I usually put the helper fuctions based where it is defined in the spec then by frequency of use, since they are both used equally. array module is best.

[dirkdev98]

Alright, will do the refactor first and implement the new functions afterwards. Thanks!