### 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/DocumentParser.java
public XContentBuilder toXContent(XContentBuilder builder, Params params) {
            throw new UnsupportedOperationException();
        }
        @Override
        protected String contentType() {
            throw new UnsupportedOperationException();
        }
    };
    private static class NoOpObjectMapper extends ObjectMapper {
        NoOpObjectMapper(String name, String fullPath) {
            super(name, fullPath, Explicit.IMPLICIT_TRUE, Explicit.IMPLICIT_TRUE, Dynamic.RUNTIME, Collections.emptyMap());
        }
    }
    /**
     * Internal version of {@link DocumentParserContext} that is aware of implementation details like nested documents
     * and how they are stored in the lucene index.
     */
    private static class RootDocumentParserContext extends DocumentParserContext {
        private final ContentPath path = new ContentPath();
        private final XContentParser parser;
        private final LuceneDocument document;
        private final List<LuceneDocument> documents = new ArrayList<>();
        private final long maxAllowedNumNestedDocs;
        private long numNestedDocs;
        private boolean docsReversed = false;
        RootDocumentParserContext(
            MappingLookup mappingLookup,
            MappingParserContext mappingParserContext,
            SourceToParse source,
            XContentParser parser