Make handling of object indices more in line with the spec

[gbrail]

• In more cases, treat out-of-range numeric indices as strings
• For typed arrays, correctly implement index semantics

This addresses many (but maybe not all) of the issues identified in #1389

[p-bakker]

Looks like this PR fixes Object.keys(x) and JSON.stringify(x) testcases, but not the JSON.parse(...) test:

js> JSON.parse('{"D": true, "-1": true, "A": true}', console.log);
INFO -1 true
INFO D true
INFO A true
INFO {}

[p-bakker]

Think JSON.parse does it wrong, because it calls Scriptruntime.indexFromString directly from JsonParser.readObject, instead of ScriptRuntime.toStringIdOrIndex()/getIndexObject()

[p-bakker]

Or its just that ScriptRuntime.indexFromString("-1") returns an odd value, namely 4294967295 instead of -1

[p-bakker]

Nice! All tests in the compat table under (ES)6 > Misc > 'own property order' (except for the ones based on Reflect) now pass!

Amazed that this doesn't unbreak some Test262 tests, but it is what it is

So, LGTM!

[rbri]

@gbrail sorry for being late at this party but while comparing your patch with my one i found one difference

org.mozilla.javascript.ScriptRuntime.getIndexObject(double)

/**
 * If d is exact int value, return its value wrapped as Integer and othewise return d converted
 * to String.
 */
static Object getIndexObject(double d) {
    int i = (int) d;
    if (i == d) {
        if (i < 0) {
            return Integer.toString(i);
        }
        return Integer.valueOf(i);
    }
    return toString(d);
}

I have added the i<0 check to this method but you not. Is this missing or have you checked that this is not needed?