### Description

It'd be lovely is a `filters` or `filter` agg that touches a `constant_keyword` would properly rewrite itself to `match_all` and `match_none` and "go fast", at least when it's at the root of the aggs tree. Theoretically it should "just work" but it doesn't seem to. Also! The `terms` agg should be able to act on there being only a single possible value. Maybe it can even act on the `match_all`/`match_none` nature of the `constant_keyword`. I'm not sure how, but it does feel like there are optimizations in there. Particularly when `terms` is the top level agg.
server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregator.java
subAggs,
                keyed,
                keyedBucket
            );
            buckets.add(bucket);
        }
        if (otherBucketKey != null) {
            InternalFilters.InternalBucket bucket = new InternalFilters.InternalBucket(otherBucketKey, 0, subAggs, keyed, keyedBucket);
            buckets.add(bucket);
        }
        return new InternalFilters(name, buckets, keyed, keyedBucket, metadata());
    }
    @Override
    public void collectDebugInfo(BiConsumer<String, Object> add) {
        super.collectDebugInfo(add);
        List<Map<String, Object>> filtersDebug = new ArrayList<>(filters.size());
        for (QueryToFilterAdapter filter : filters) {
            Map<String, Object> debug = new HashMap<>();
            filter.collectDebugInfo(debug::put);
            filtersDebug.add(debug);
        }
        add.accept("filters", filtersDebug);
    }
    /**
     * Collects results by building a {@link LongPredicate} per filter and testing if
     * each doc sent to its {@link LeafBucketCollector} is in each filter
     * which is generally slower than {@link FilterByFilterAggregator} but is compatible
     * with parent and child aggregations.
     */
    static class Compatible extends FiltersAggregator {