Right now filter aggregations run in "compatible" mode if the top level query is `bool: {filter: { match_all: {}}}}` - but this really just just `match_all` in disguise. We should just run in filter-by-filter mode here.
server/src/test/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregatorTests.java
import org.elasticsearch.index.query.TermQueryBuilder;
import org.elasticsearch.index.shard.ShardId;
import org.elasticsearch.search.aggregations.AggregationBuilder;
import org.elasticsearch.search.aggregations.AggregationReduceContext;
import org.elasticsearch.search.aggregations.Aggregator;
import org.elasticsearch.search.aggregations.AggregatorTestCase;
import org.elasticsearch.search.aggregations.InternalAggregation;
import org.elasticsearch.search.aggregations.LeafBucketCollector;
import org.elasticsearch.search.aggregations.bucket.filter.FiltersAggregator.KeyedFilter;
import org.elasticsearch.search.aggregations.bucket.nested.NestedAggregatorTests;
import org.elasticsearch.search.aggregations.metrics.Max;
import org.elasticsearch.search.aggregations.metrics.MaxAggregationBuilder;
import org.elasticsearch.search.aggregations.metrics.Sum;
import org.elasticsearch.search.aggregations.metrics.SumAggregationBuilder;
import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.PipelineTree;
import org.elasticsearch.search.aggregations.support.AggregationContext;
import org.elasticsearch.search.aggregations.support.AggregationInspectionHelper;
import org.elasticsearch.search.internal.ContextIndexSearcherTests.DocumentSubsetDirectoryReader;
import org.elasticsearch.test.MapMatcher;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.function.IntFunction;
import static org.elasticsearch.test.ListMatcher.matchesList;