Implement Array.prototype.copyWithin

[jedel1043]

This Pull Request checks off a method from #36.

It changes the following:

• Adds the method Array.prototype.copyWithin
• Adds a test for said method

Had to take a few liberties to make the code more readable, but it should be spec compliant nonetheless. Please tell me if I overlooked something to fix it asap.

[Razican]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	78,897	78,897	0
Passed	26,865	26,919	+54
Ignored	15,628	15,628	0
Failed	36,404	36,350	-54
Panics	0	0	0
Conformance	34.05%	34.12%	+0.07%

Fixed tests:

test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-target.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-target.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/undefined-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/undefined-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/length-near-integer-limit.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/length-near-integer-limit.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-target.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-target.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-start-change-target.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-target.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-target.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-target.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-target.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-target-and-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-target-and-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-get-start-value.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-get-start-value.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/name.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/name.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-target-and-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-target-and-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/call-with-boolean.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/call-with-boolean.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/negative-out-of-bounds-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-target-start-and-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-start.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-start.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/coerced-values-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-set-target-value.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-set-target-value.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-this.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-this.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-this-length.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-this-length.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-end.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/non-negative-out-of-bounds-end.js (previously Failed)
test/built-ins/Array/prototype/copyWithin/prop-desc.js [strict mode] (previously Failed)
test/built-ins/Array/prototype/copyWithin/prop-desc.js (previously Failed)
test/built-ins/Number/S9.3.1_A3_T2.js [strict mode] (previously Failed)
test/built-ins/Number/S9.3.1_A3_T2.js (previously Failed)
test/built-ins/Number/S9.3.1_A3_T1.js [strict mode] (previously Failed)
test/built-ins/Number/S9.3.1_A3_T1.js (previously Failed)

Broken tests:

test/built-ins/Array/prototype/copyWithin/return-abrupt-from-delete-target.js [strict mode] (previously Passed)
test/built-ins/Array/prototype/copyWithin/return-abrupt-from-delete-target.js (previously Passed)
test/built-ins/Number/prototype/toExponential/this-is-0-fractiondigits-is-0.js [strict mode] (previously Passed)
test/built-ins/Number/prototype/toExponential/this-is-0-fractiondigits-is-0.js (previously Passed)

[RageKnify]

Looks good, looking at the spec, seems like our implementations of has_field and remove_property aren't enough, since it should be possible for them to throw.
We should open an issue for that, but I think this implementation is good right now, maybe add some TODO comments around lines 1595 and 1599.

[Razican]

Let's merge it! Thanks!