Implement Array findLast and findLastIndex

[bsinky]

This Pull Request closes #1654.

It changes the following:

• Implements Array.prototype.findLast
• Implements Array.prototype.findLastIndex.

[jedel1043]

Great work! Just some small nitpicks that are easily solvable. Everything else looks good!

[jedel1043]

Test262 conformance changes:

Test result	main count	PR count	difference
Total	86,438	86,438	0
Passed	37,764	37,814	+50
Ignored	19,022	19,022	0
Failed	29,652	29,602	-50
Panics	0	0	0
Conformance	43.69%	43.75%	+0.06%

Fixed tests (50):

test/built-ins/Array/prototype/findLastIndex/predicate-called-for-each-array-property.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/predicate-called-for-each-array-property.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/name.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/name.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/predicate-not-called-on-empty-array.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/predicate-not-called-on-empty-array.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-abrupt-from-this-length.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-abrupt-from-this-length.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-negative-one-if-predicate-returns-false-value.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-negative-one-if-predicate-returns-false-value.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-abrupt-from-property.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-abrupt-from-property.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/length.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/length.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-index-predicate-result-is-true.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-index-predicate-result-is-true.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-abrupt-from-predicate-call.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/return-abrupt-from-predicate-call.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/prop-desc.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/prop-desc.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/array-altered-during-loop.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/array-altered-during-loop.js (previously Failed)
test/built-ins/Array/prototype/findLastIndex/predicate-call-this-strict.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/call-with-boolean.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLastIndex/call-with-boolean.js (previously Failed)
test/built-ins/Array/prototype/findLast/predicate-called-for-each-array-property.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/predicate-called-for-each-array-property.js (previously Failed)
test/built-ins/Array/prototype/findLast/name.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/name.js (previously Failed)
test/built-ins/Array/prototype/findLast/predicate-not-called-on-empty-array.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/predicate-not-called-on-empty-array.js (previously Failed)
test/built-ins/Array/prototype/findLast/return-abrupt-from-this-length.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/return-abrupt-from-this-length.js (previously Failed)
test/built-ins/Array/prototype/findLast/return-abrupt-from-property.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/return-abrupt-from-property.js (previously Failed)
test/built-ins/Array/prototype/findLast/length.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/length.js (previously Failed)
test/built-ins/Array/prototype/findLast/return-undefined-if-predicate-returns-false-value.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/return-undefined-if-predicate-returns-false-value.js (previously Failed)
test/built-ins/Array/prototype/findLast/return-abrupt-from-predicate-call.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/return-abrupt-from-predicate-call.js (previously Failed)
test/built-ins/Array/prototype/findLast/prop-desc.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/prop-desc.js (previously Failed)
test/built-ins/Array/prototype/findLast/array-altered-during-loop.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/array-altered-during-loop.js (previously Failed)
test/built-ins/Array/prototype/findLast/return-found-value-predicate-result-is-true.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/return-found-value-predicate-result-is-true.js (previously Failed)
test/built-ins/Array/prototype/findLast/predicate-call-this-strict.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/call-with-boolean.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/findLast/call-with-boolean.js (previously Failed)

[bsinky]

Thanks for the suggestions! They should all be updated now. I left the comments as-is, the implementation is different but at least they show how it matches up with the proposal.

[jedel1043]

Nice work! Looks good to me 😁