### Description

Follow-up of #98360: when there is a single filter, the collector could save the overhead of the priority queue (both in `collect()` and `competitiveIterator()`), which would likely result in a speedup.
server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregator.java
new FilterByFilterAggregator.AdapterBuilder<FilterByFilterAggregator>(
                name,
                keyed,
                keyedBucket,
                otherBucketKey,
                context,
                parent,
                cardinality,
                metadata
            ) {
                @Override
                protected FilterByFilterAggregator adapt(
                    CheckedFunction<AggregatorFactories, FilterByFilterAggregator, IOException> delegate
                ) throws IOException {
                    return delegate.apply(factories);
                }
            };
        for (QueryToFilterAdapter f : filters) {
            filterByFilterBuilder.add(f);
        }
        FilterByFilterAggregator filterByFilter = filterByFilterBuilder.build();
        if (filterByFilter != null) {
            return filterByFilter;
        }
        return new FiltersAggregator.Compatible(
            name,
            factories,
            filters,
            keyed,
            keyedBucket,