[solver] Move internals to `Thyra` objects

[maxfirmbach]

Description

Currently the iterative solver specifically relies on the fact that we inherit our SparseOperator from an Epetra_Operator implementing Apply() and ApplyInverse() for the block matrix implementation.
By switching the solver internals to Thyra and wrap them into the correct data structure should avoid this issue and should make it possible to cut the inheritance to Epetra_Operator. In addition it would simplify the construction of the linear solver with Stratimikos. If implemented correctly we should be able to switch to Tpetra without touching the linear solver internals at all.

Possible Solution and Definition of Done

• Delete the epetra_operator() method
• Provide a conversion utility functions for SparseMatrix, BlockSparseMatrix, Map, MultiVector and wrap the data types into the respective Thyra based type (see #[LinAlg] Cleanup of sparse matrix implementations #1525)
• Refactor the preconditioner classes to hold a Thyra::LinearOp as internal member instead of an Epetra_Operator
  • Use Thyra for Teko based preconditioner
  • Use Thyra for Ifpack based preconditioner (see [Ifpack] Move backend to Stratimikos #766 [solver] Move Ifpack preconditioner construction to Stratimikos #1406)
  • Use Thyra for MueLu based preconditioner (see [MueLu] Move backend to Stratimikos #1401)
  • Use Thyra for LinalgPrecondOperator projection (see [Solver] Move LinalgPrecondOperator to Thyra #1642)
• Refactor the iterative solver to use Thyra based objects instead of Epetra ones (see [solver] Rework setup and solve input arguments #1550 [MueLu] Move single field multigrid to Stratimikos #1572 [WIP] Move iterative solver interface and internals to Thyra #1594)

Interested Parties