feat(typescript): Improve adapter typings

[daffl]

This is a follow-up to #2600 and closes #2564.

It updates the adapter types with the proper overloads, most importantly returning an array when passing { paginate: false }. It also adds an AdapterBase service from which other adapters can now extend implementing only the hook-less service methods and no service interface. The reason is that generated services will now extend from those and then implement the official service methods which will by default in turn call their internal counterpart. This allows to implement the service methods you want with different parameter types and return values without being restricted by any incompatible interfaces.

export class UserService extends MemoryAdapter<UserResult, UserData, UserServiceParams> {
  async find (params?: UserServiceParams & { paginate?: PaginationOptions }): Promise<Paginated<T>>;
  async find (params?: UserServiceParams & { paginate: false }): Promise<UserResult[]>;
  async find (params?: UserServiceParams): Promise<Paginated<UserResult>|UserResult[]>;
  async find (params?: UserServiceParams): Promise<Paginated<UserResult>|UserResult[]> {
    return this._find(params);
  }

  async get (id: Id, params?: UserServiceParams) {
    return {
      id,
      message: 'I can return whatever I want here'
    };
  }

  async create (data: UserCreateData, params?: UserServiceParams) {
    return this._create(data, params);
  }

  async update (id: Id, data: D, params?: UserServiceParams): Promise<T> {
    return this._update(id, data, params);
  }

  async patch (id: Id, data: Partial<D>, params?: UserServiceParams): Promise<UserResult>;
  async patch (id: null, data: Partial<D>, params?: UserServiceParams): Promise<UserResult[]>;
  async patch (id: NullableId, data: Partial<D>, params?: UserServiceParams): Promise<UserResult | UserResult[]> {
    return this._patch(id, data, params);
  }

  async remove (id: Id, params?: UserServiceParams): Promise<UserResult>;
  async remove (id: null, params?: UserServiceParams): Promise<UserResult[]>;
  async remove (id: NullableId, params?: UserServiceParams): Promise<UserResult | UserResult[]> {
    return this._remove(id, params);
  }
}