New vector APIs for hypre_IJVector

[victorapm]

This PR introduces new public APIs and internal functions in hypre to allow users to directly assign external data pointers to IJ vectors, which is useful for applications that wish to avoid additional memory allocations or copies by reusing pre-existing data arrays.

The new key APIs are HYPRE_IJVectorInitializeShell for setting up HYPRE_IJVector metadata without doing any memory allocations and HYPRE_IJVectorInitializeData for assigning an external data array to the vector structure.

Example usage:

      // Data array is allocated and set

      HYPRE_IJVector ij_vec;
      HYPRE_IJVectorCreate(comm, ilower, iupper, &ij_vec);
      HYPRE_IJVectorSetObjectType(ij_vec, HYPRE_PARCSR);
      HYPRE_IJVectorInitializeShell(ij_vec);
      HYPRE_IJVectorInitializeData(ij_vec, data);
      HYPRE_IJVectorAssemble(ij_vec);

[rfalgout]

Looks good! Thanks!