Array fixes

[romainmenke]

Fixes for Array

IE8

• check for Symbol in _ESAbstract/ToInteger [1]
• Array.sort stable fix must check for ownProperty [2]

IE8 does not get the Symbol.prototype.description polyfill.

IE9-11

• Array.prototype.@@iterator fail will be fixed with a Symbol refactor [3]
• Array.prototype.entries fail will be fixed with a Symbol refactor [3]
• Array.prototype.keys fail will be fixed with a Symbol refactor [3]

Other browsers

did some spot tests for older chrome/firefox/safari versions

These show the same results as IE9-11.

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Notes :

(1) Array.prototype.flat uses ToInteger which lacked a check for Symbol.
This test is skipped when self.Symbol doesn't exist.

(2) Array.prototype.sort has a fix for stable sorting.
This uses a for .. in iteration which didn't have a check for ownProperty.

On master :

for (var a in that) {
    console.log(a);
    if (that[a].item !== this[a]) {
        this[a] = that[a].item;
    }
}

This is not ideal, but didn't throw before.
When all polyfills are loaded and Array.prototype is fully polyfilled it does throw when handing one of the inherited properties.

(3) Symbol.iterator is undefined because Symbol.prototype.description uses a wrapper to intercept the arguments.
This wrapper does not restore the static methods on Symbol.

Symbol.iterator being missing breaks some Array methods which rely on iterators.
This will not be fixed in this branch.