### 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/test/java/org/elasticsearch/index/mapper/DynamicMappingTests.java
"foo": {
                    "properties": {
                      "bar": {
                        "type": "text",
                        "fields": {
                          "keyword": {
                            "type": "keyword",
                            "ignore_above": 256
                          }
                        }
                      },
                      "baz": {
                        "type": "long"
                      }
                    }
                  }
                }
              }
            }"""), Strings.toString(doc.dynamicMappingsUpdate()));
    }
    public void testReuseExistingMappings() throws Exception {
        
        
        DocumentMapper newMapper = createDocumentMapper(mapping(b -> {
            b.startObject("my_field1").field("type", "text").field("store", "true").endObject();
            b.startObject("my_field2").field("type", "integer").field("store", "false").endObject();
            b.startObject("my_field3").field("type", "long").field("doc_values", "false").endObject();
            b.startObject("my_field4").field("type", "float").field("index", "false").endObject();
            b.startObject("my_field5").field("type", "double").field("store", "true").endObject();
            b.startObject("my_field6").field("type", "date").field("doc_values", "false").endObject();