getByAccountId(accountId) {
        const entityIndex = this._accountNumberToEntity.get(accountId);
        if (entityIndex === undefined)
            return null;
        return this.entities.get(entityIndex);
    }
Returns the entity that belongs to the player with a given Steam account ID.
@param {number} accountId - Steam account ID
@returns {Player|null} Entity referenced by the account ID. `null` if no matching player.