### 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
private final XContentParserConfiguration parserConfiguration;
    private final Supplier<DocumentParsingObserver> documentParsingObserverSupplier;
    private final MappingParserContext mappingParserContext;
    DocumentParser(
        XContentParserConfiguration parserConfiguration,
        MappingParserContext mappingParserContext,
        Supplier<DocumentParsingObserver> documentParsingObserverSupplier
    ) {
        this.mappingParserContext = mappingParserContext;
        this.parserConfiguration = parserConfiguration;
        this.documentParsingObserverSupplier = documentParsingObserverSupplier;
    }
    /**
     * Parse a document
     *
     * @param source        the document to parse
     * @param mappingLookup the mappings information needed to parse the document
     * @return the parsed document
     * @throws DocumentParsingException whenever there's a problem parsing the document
     */
    public ParsedDocument parseDocument(SourceToParse source, MappingLookup mappingLookup) throws DocumentParsingException {
        if (source.source() != null && source.source().length() == 0) {
            throw new DocumentParsingException(new XContentLocation(0, 0), "failed to parse, document is empty");
        }
        final RootDocumentParserContext context;
        final XContentType xContentType = source.getXContentType();