### 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
dateFt,
            intFt
        );
    }
    public void testDocValuesFieldExistsForDate() throws IOException {
        DateFieldMapper.DateFieldType ft = new DateFieldMapper.DateFieldType("f");
        QueryBuilder exists;
        if (randomBoolean()) {
            exists = new ExistsQueryBuilder("f");
        } else {
            
            exists = new RangeQueryBuilder("f").gte("2020-01-01").lt("2020-01-02");
        }
        long start = DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.parseMillis("2020-01-01T00:00:01");
        docValuesFieldExistsTestCase(exists, ft, true, i -> {
            long date = start + TimeUnit.HOURS.toMillis(i);
            return List.of(new LongPoint("f", date), new NumericDocValuesField("f", date));
        });
    }
    public void testDocValuesFieldExistsForDateWithMultiValuedFields() throws IOException {
        DateFieldMapper.DateFieldType ft = new DateFieldMapper.DateFieldType("f");
        long start = DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.parseMillis("2020-01-01T00:00:01");
        docValuesFieldExistsTestCase(new ExistsQueryBuilder("f"), ft, true, i -> {
            long date = start + TimeUnit.HOURS.toMillis(i);
            return List.of(
                new LongPoint("f", date),
                new LongPoint("f", date + 10),
                new SortedNumericDocValuesField("f", date),
                new SortedNumericDocValuesField("f", date + 10)
            );