### Description

Dynamic mappings can greatly help the getting started experience but they currently don't apply to all types, one example is `dense_vector`.

It's been suggested to automatically map float arrays as dense vectors when there are more than 100 values, or a heuristic along these lines.
server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java
private BinaryDocValues values;
        private boolean hasValue;
        private final IndexVersion indexCreatedVersion;
        private DocValuesSyntheticFieldLoader(IndexVersion indexCreatedVersion) {
            this.indexCreatedVersion = indexCreatedVersion;
        }
        @Override
        public Stream<Map.Entry<String, StoredFieldLoader>> storedFieldLoaders() {
            return Stream.of();
        }
        @Override
        public DocValuesLoader docValuesLoader(LeafReader leafReader, int[] docIdsInLeaf) throws IOException {
            values = leafReader.getBinaryDocValues(name());
            if (values == null) {