### Description

Our most common aggregations should be optimized for single-valued fields. In general, our aggregations look like this:

```java
    @Override
    public LeafBucketCollector getLeafCollector(LeafReaderContext ctx, LeafBucketCollector sub) throws IOException {
        if (valuesSource == null) {
            return LeafBucketCollector.NO_OP_COLLECTOR;
        }
        SortedNumericDocValues values = valuesSource.longValues(ctx);
        return new LeafBucketCollectorBase(sub, values) {
            @Override
            public void collect(int doc, long owningBucketOrd) throws IOException {
                if (values.advanceExact(doc)) {
                    int valuesCount = values.docValueCount();
                    for (int i = 0; i < valuesCount; ++i) {
                        long value = values.nextValue();
                        // do something with value
                    }
                }
            }
        };
    }
```

The idea consists of optimizing for single-valued fields by unwrapping the single-valued doc-value iterator:

```java
    @Override
    public LeafBucketCollector getLeafCollector(LeafReaderContext ctx, LeafBucketCollector sub) throws IOException {
        if (valuesSource == null) {
            return LeafBucketCollector.NO_OP_COLLECTOR;
        }
        SortedNumericDocValues values = valuesSource.longValues(ctx);
        NumericDocValues singleValues = DocValues.unwrapSingleton(values); // or FieldData.unwrapSingleton for doubles
        if (singleValues != null) {
            return new LeafBucketCollectorBase(sub, values) {
                @Override
                public void collect(int doc, long owningBucketOrd) throws IOException {
                    if (singleValues.advanceExact(doc)) {
                        long value = singleValues.longValue();
                        // do something with value
                    }
                }
            };
        } else {
            return new LeafBucketCollectorBase(sub, values) {
                @Override
                public void collect(int doc, long owningBucketOrd) throws IOException {
                    if (values.advanceExact(doc)) {
                        int valuesCount = values.docValueCount();
                        for (int i = 0; i < valuesCount; ++i) {
                            long value = values.nextValue();
                            // do something with value
                        }
                    }
                }
            };
        }
    }
```

The `terms` aggregation already does this, and e.g. `min` and `max` aggregations use similar tricks that also help optimize the single-valued case. But `date_histogram`, which is one of our most common aggregations, doesn't. Let's specialize the single-value case for date histograms too?
server/src/test/java/org/elasticsearch/search/aggregations/bucket/range/RangeAggregatorTests.java
private static final String NUMBER_FIELD_NAME = "number";
    private static final String DATE_FIELD_NAME = "date";
    public void testNoMatchingField() throws IOException {
        testCase(new MatchAllDocsQuery(), iw -> {
            iw.addDocument(singleton(new SortedNumericDocValuesField("bogus_field_name", 7)));
            iw.addDocument(singleton(new SortedNumericDocValuesField("bogus_field_name", 2)));
            iw.addDocument(singleton(new SortedNumericDocValuesField("bogus_field_name", 3)));
        }, range -> {
            List<? extends InternalRange.Bucket> ranges = range.getBuckets();
            assertEquals(2, ranges.size());
            assertEquals(0, ranges.get(0).getDocCount());
            assertEquals(0, ranges.get(1).getDocCount());
            assertFalse(AggregationInspectionHelper.hasValue(range));
        });
    }
    public void testMatchesSortedNumericDocValues() throws IOException {
        testCase(new MatchAllDocsQuery(), iw -> {
            iw.addDocument(List.of(new SortedNumericDocValuesField(NUMBER_FIELD_NAME, 7), new IntPoint(NUMBER_FIELD_NAME, 7)));
            iw.addDocument(List.of(new SortedNumericDocValuesField(NUMBER_FIELD_NAME, 2), new IntPoint(NUMBER_FIELD_NAME, 2)));
            iw.addDocument(List.of(new SortedNumericDocValuesField(NUMBER_FIELD_NAME, 3), new IntPoint(NUMBER_FIELD_NAME, 3)));
        }, range -> {
            List<? extends InternalRange.Bucket> ranges = range.getBuckets();
            assertEquals(2, ranges.size());
            assertEquals(2, ranges.get(0).getDocCount());
            assertEquals(0, ranges.get(1).getDocCount());
            assertTrue(AggregationInspectionHelper.hasValue(range));