message: Add using EnableLinOp<Diagonal>::convert_to/move_to
diff: @@ -64,21 +64,24 @@ class Dense;
  * @ingroup LinOp
  */
  template <typename ValueType = default_precision>
  -class Diagonal : public ConvertibleTo<Csr<ValueType, int32>>,
  - public ConvertibleTo<Csr<ValueType, int64>>,
  - public EnableLinOp<Diagonal<ValueType>>,
  +class Diagonal : public EnableLinOp<Diagonal<ValueType>>,
  public EnableCreateMethod<Diagonal<ValueType>>,
  + public ConvertibleTo<Csr<ValueType, int32>>,
  + public ConvertibleTo<Csr<ValueType, int64>>,
  public Transposable,
  public WritableToMatrixData<ValueType, int32>,
  public WritableToMatrixData<ValueType, int64>,
  public ReadableFromMatrixData<ValueType, int32>,
  public ReadableFromMatrixData<ValueType, int64> {
  - friend class Csr<ValueType, int32>;
  - friend class Csr<ValueType, int64>;
  friend class EnablePolymorphicObject<Diagonal, LinOp>;
  friend class EnableCreateMethod<Diagonal>;
  + friend class Csr<ValueType, int32>;
  + friend class Csr<ValueType, int64>;
  public:
  + using EnableLinOp<Diagonal>::convert_to;
  + using EnableLinOp<Diagonal>::move_to;
  +
  using value_type = ValueType;
  using index_type = int64;
  using mat_data = gko::matrix_data<ValueType, int64>;
  