### Description

InternalComposite.formatObject() can throw an IllegalArgumentException if the format to be applied to a composite key leads to a loss of information (eg, a date histogram with a width of one day is then given a date format of 'YYYY-mm', meaning that multiple buckets from the same month would produce the same key).  This is currently only checked during serialization, meaning that we can do a great deal of work building aggregations only to then throw the result away at the end.  This also causes a problem for converting the `_search` endpoint to using chunked xcontent serialization, as the HTTP response code is the first thing sent back, and so errors that occur during later serialization don't get handled correctly.
server/src/main/java/org/elasticsearch/search/aggregations/bucket/composite/InternalComposite.java
name,
            size,
            sourceNames,
            formats,
            newBuckets,
            afterKey,
            reverseMuls,
            missingOrders,
            earlyTerminated,
            getMetadata()
        );
    }
    @Override
    public InternalBucket createBucket(InternalAggregations aggregations, InternalBucket prototype) {
        return new InternalBucket(
            prototype.sourceNames,
            prototype.formats,
            prototype.key,
            prototype.reverseMuls,
            prototype.missingOrders,
            prototype.docCount,
            aggregations
        );
    }
    public int getSize() {
        return size;
    }
    @Override
    public List<InternalBucket> getBuckets() {
        return buckets;