MatView(): do not print block size twice

MatAssemblyEnd(): fix missing space in -info

Mat: set appropriate NO_OFF_PROC_ENTRIES to bypass MPI_Allreduce()

- Replace MatMissingDiagonal() and MatMarkDiagonals_SeqXXX() with MatGetDiagonalMarkers_SeqXXX()

- Mat_SeqXXX->diag is not automatically created during MatAssemblyEnd() saving memory and time

- Replace MatMissingDiagonal() and MatMarkDiagonals_SeqXXX() with MatGetDiagonalMarkers_SeqXXX()

- Mat_SeqXXX->diag is not automatically created during MatAssemblyEnd() saving memory and time

- Accessing Mat_SeqXXX->diag now requires the use of MatGetDiagonalMarkers_SeqXXX() except when the current values are known to be correct; for example during numerical factorizations and solves

- Mat_SeqXXX->diag is now never shared among matrices; hence the free_diag flag is gone. That was always a risky proposition since any of the owning matrices could chang the values thus making them incorrect for other owners.

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Fix outdated output of MatView() for nest matrix with ASCII

Now matches VecNest version and does not have outdated reprinting of Mat Object and type

MATIS: implement ZeroRowsLocal and ZeroRowsColumnsLocal local reference

add tests

MAT test ex125: add failing test for superlu_dist

MatSetValuesHash: support ignorezeroentries

Fix ubsan output

Remove explicitly listed empty files and switch to output/empty.out