### 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
}
    public void testDynamicMappingsNotNeeded() throws Exception {
        DocumentMapper mapper = createDocumentMapper(fieldMapping(b -> b.field("type", "text")));
        ParsedDocument doc = mapper.parse(source(b -> b.field("field", "bar")));
        
        assertNull(doc.dynamicMappingsUpdate());
    }
    public void testDynamicField() throws Exception {
        DocumentMapper mapper = createDocumentMapper(mapping(b -> {}));
        ParsedDocument doc = mapper.parse(source(b -> b.field("foo", "bar")));
        assertNotNull(doc.dynamicMappingsUpdate());
        assertEquals(XContentHelper.stripWhitespace("""
            {
              "_doc": {
                "properties": {
                  "foo": {
                    "type": "text",
                    "fields": {
                      "keyword": {
                        "type": "keyword",
                        "ignore_above": 256
                      }
                    }
                  }
                }
              }
            }"""), Strings.toString(doc.dynamicMappingsUpdate()));
    }
    public void testDynamicFieldOnIncorrectDate() throws Exception {
        DocumentMapper mapper = createDocumentMapper(mapping(b -> {}));