### 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/test/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregatorTests.java
null,
            Collections.emptyMap()
        );
        MappedFieldType intFt = new NumberFieldMapper.NumberFieldType("int", NumberType.INTEGER);
        AggregationBuilder builder = new FiltersAggregationBuilder(
            "test",
            new KeyedFilter("q1", new RangeQueryBuilder("test").from("2010-01-01").to("2010-03-01").includeUpper(false)),
            new KeyedFilter("q2", new RangeQueryBuilder("test").from("2020-01-01").to("2020-03-01").includeUpper(false))
        ).subAggregation(new MaxAggregationBuilder("m").field("int")).subAggregation(new SumAggregationBuilder("s").field("int"));
        List<List<IndexableField>> docs = new ArrayList<>();
        docs.add(
            List.of(
                new LongPoint("test", DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.parseMillis("2010-01-02")),
                new SortedNumericDocValuesField("int", 100)
            )
        );
        docs.add(
            List.of(
                new LongPoint("test", DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.parseMillis("2020-01-02")),
                new SortedNumericDocValuesField("int", 5)
            )
        );
        docs.add(
            List.of(
                new LongPoint("test", DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.parseMillis("2020-01-03")),
                new SortedNumericDocValuesField("int", 10)
            )
        );
        /*
         * Shuffle the docs so we collect them in a random order which causes