### 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
assertThat(path2, instanceOf(ObjectMapper.class));
            Mapper path3 = ((ObjectMapper) path2).getMapper("path3");
            assertThat(path3, instanceOf(ObjectMapper.class));
            assertFalse(path3.iterator().hasNext());
        }
        assertNull(doc.rootDoc().getField("path1.path2.path3.field"));
        merge(mapperService, dynamicMapping(doc.dynamicMappingsUpdate()));
        Mapping merged = mapperService.documentMapper().mapping();
        {
            Mapper path1 = merged.getRoot().getMapper("path1");
            assertThat(path1, instanceOf(ObjectMapper.class));
            Mapper path2 = ((ObjectMapper) path1).getMapper("path2");
            assertThat(path2, instanceOf(ObjectMapper.class));
            Mapper path3 = ((ObjectMapper) path2).getMapper("path3");
            assertThat(path3, instanceOf(ObjectMapper.class));
            assertFalse(path3.iterator().hasNext());
        }
        assertEquals(1, merged.getRoot().runtimeFields().size());
        assertNotNull(merged.getRoot().getRuntimeField("path1.path2.path3.field"));
    }
    public void testIncremental() throws Exception {
        
        
        DocumentMapper mapper = createDocumentMapper(fieldMapping(b -> b.field("type", "text")));
        ParsedDocument doc = mapper.parse(source(b -> {
            b.field("field", "bar");
            b.field("bar", "baz");
        }));
        assertNotNull(doc.dynamicMappingsUpdate());
        assertThat(Strings.toString(doc.dynamicMappingsUpdate()), containsString("{\"bar\":"));