### 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/DocumentParserContext.java
public LuceneDocument rootDoc() {
            return in.rootDoc();
        }
        @Override
        public LuceneDocument doc() {
            return in.doc();
        }
        @Override
        protected void addDoc(LuceneDocument doc) {
            in.addDoc(doc);
        }
    }
    private final MappingLookup mappingLookup;
    private final MappingParserContext mappingParserContext;
    private final SourceToParse sourceToParse;
    private final Set<String> ignoredFields;
    private final List<Mapper> dynamicMappers;
    private final Set<String> newFieldsSeen;
    private final Map<String, ObjectMapper> dynamicObjectMappers;
    private final List<RuntimeField> dynamicRuntimeFields;
    private final DocumentDimensions dimensions;
    private final ObjectMapper parent;
    private final ObjectMapper.Dynamic dynamic;
    private String id;
    private Field version;
    private SeqNoFieldMapper.SequenceIDFields seqID;
    private DocumentParserContext(
        MappingLookup mappingLookup,
        MappingParserContext mappingParserContext,
        SourceToParse sourceToParse,