### 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/DocumentParserContext.java
}
        private State state = State.FIELD;
        private final String field;
        CopyToParser(String fieldName, XContentParser in) {
            super(in);
            this.field = fieldName;
            assert in.currentToken().isValue() || in.currentToken() == Token.VALUE_NULL;
        }
        @Override
        public Token nextToken() throws IOException {
            if (state == State.FIELD) {
                state = State.VALUE;
                return delegate().currentToken();
            }
            return Token.END_OBJECT;
        }
        @Override
        public Token currentToken() {
            if (state == State.FIELD) {
                return Token.FIELD_NAME;
            }
            return delegate().currentToken();
        }
        @Override
        public String currentName() throws IOException {
            return field;
        }
    }
}