### 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":{"type":"text\""""));
    }
    public void testInnerDynamicMapping() throws Exception {
        DocumentMapper mapper = createDocumentMapper(fieldMapping(b -> b.field("type", "object")));
        ParsedDocument doc = mapper.parse(source(b -> {
            b.startObject("field");
            {
                b.startObject("bar").field("baz", "foo").endObject();
            }
            b.endObject();
        }));
        assertNotNull(doc.dynamicMappingsUpdate());
        assertThat(Strings.toString(doc.dynamicMappingsUpdate()), containsString("""
            {"field":{"properties":{"bar":{"properties":{"baz":{"type":"text\""""));
    }
    public void testComplexArray() throws Exception {
        DocumentMapper mapper = createDocumentMapper(mapping(b -> {}));
        ParsedDocument doc = mapper.parse(source(b -> {
            b.startArray("foo");
            {
                b.startObject().field("bar", "baz").endObject();
                b.startObject().field("baz", 3).endObject();
            }
            b.endArray();
        }));
        assertNotNull(doc.dynamicMappingsUpdate());
        assertEquals(XContentHelper.stripWhitespace("""
            {
              "_doc": {
                "properties": {