`set`  doesn't exist on Map

Hi, the set doesn't exist on the map
```
const docA = new LoroDoc();
const mapA = docA.getMap("map");

mapA.set("a", 1);
```

Currently I can see only
```
    insert(key: string, value: Value): void;
mapA.insert("a", 1);
```

also
```
mapA.get("a");
```
doesn't return the value