MueLu: migrate HHG driver to Xpetra

Created by: mayrmt

@trilinos/muelu

Expectations

Switch from Epetra stack to Xpetra (or Tpetra if Xpetra is to much trouble).

Current Behavior

The MueLu/HHG driver in packages/muelu/research/mmayr/composite_to_regions/src/main.cpp is fully implemented using the old Epetra stack.

Motivation and Context

@lucbv's performance improvements for structured grid's rely on Kokkos. To enable them in the HHG driver, we need to migrate the driver at least to Tpetra. Let's try to use Xpetra for better MueLu compatibility.

Definition of Done

• Completely switch from Epetra to Xpetra (or Tpetra as fall back)
• Update CMake dependencies accordingly

Possible Solution

Replace Epetra stuff by corresponding Xpetra stuff.