3.1.7.1 OrdinaryOwnMetadataKeys(O, P) https://rbuckton.github.io/reflect-metadata/#ordinaryownmetadatakeys
function OrdinaryOwnMetadataKeys(O, P) {
            var keys = [];
            var metadataMap = GetOrCreateMetadataMap(O, P, /*Create*/ false);
            if (IsUndefined(metadataMap))
                return keys;
            var keysObj = metadataMap.keys();
            var iterator = GetIterator(keysObj);
            var k = 0;
            while (true) {
                var next = IteratorStep(iterator);
                if (!next) {
                    keys.length = k;
                    return keys;
                }
                var nextValue = IteratorValue(next);
                try {
                    keys[k] = nextValue;
                }
                catch (e) {
                    try {
                        IteratorClose(iterator);
                    }
                    finally {
                        throw e;
                    }
                }
                k++;
            }
        }