### 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
switch (token) {
                case FIELD_NAME:
                    currentFieldName = parser.currentName();
                    if (currentFieldName.isEmpty()) {
                        throw new IllegalArgumentException("Field name cannot be an empty string");
                    }
                    if (currentFieldName.isBlank()) {
                        throwFieldNameBlank(context, currentFieldName);
                    }
                    break;
                case START_OBJECT:
                    parseObject(context, currentFieldName);
                    break;
                case START_ARRAY:
                    parseArray(context, currentFieldName);
                    break;
                case VALUE_NULL:
                    parseNullValue(context, currentFieldName);
                    break;
                default:
                    if (token.isValue()) {
                        parseValue(context, currentFieldName);
                    }
                    break;
            }
            token = parser.nextToken();
        }
    }
    private static void throwFieldNameBlank(DocumentParserContext context, String currentFieldName) {
        throw new DocumentParsingException(