### 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
List.of(new LongPoint("test", DateFieldMapper.DEFAULT_DATE_TIME_FORMATTER.parseMillis("2020-01-02")))
                )
            );
        }, searcher -> {
            debugTestCase(
                builder,
                new MatchAllDocsQuery(),
                searcher,
                (InternalFilters filters, Class<? extends Aggregator> impl, Map<String, Map<String, Object>> debug) -> {
                    assertThat(filters.getBuckets(), hasSize(1));
                    assertThat(filters.getBucketByKey("q1").getDocCount(), equalTo(1L));
                    assertThat(impl, equalTo(FilterByFilterAggregator.class));
                    assertMap(
                        debug,
                        matchesMap().entry(
                            "test",
                            matchesMap().entry("segments_with_doc_count_field", 0)
                                .entry("segments_with_deleted_docs", 0)
                                .entry("segments_collected", 0)
                                .entry("segments_counted", greaterThanOrEqualTo(1))
                                .entry(
                                    "filters",
                                    matchesList().item(
                                        matchesMap().entry("query", "test:[1577836800000 TO 1583020799999]")
                                            .entry("segments_counted_in_constant_time", 1)
                                    )
                                )
                        )
                    );
                },