ex18: fix potentially unset options->interpolate

DMPlexOrientCell_Internal: fix arg type (PetscInt -> PetscBool)

DMPlexOrientInterface: fix a leak

TODO examples failing due to wrong SF

some 'may be used uninitialized' prevention

ex18: 4_tet_test_orient tests different initial orientations

ex18: CreateMesh: remove unused arg testNum

ex18: check -distribute 1 is set if -interpolate parallel is set

ex18: hotfix SF for test 4_tet%

DMPlexInterpolate: orientation fix can be optionally turned off from options

DMPlexOrientCell_Internal factored out from DMPlexOrientCell

rename DMPlexOrientPointSF_Internal -> DMPlexOrientInterface and publish in dmpleximpl.h

DMPlexCheckPointSF: swap the two conditions

DMPlexOrientCell: added sanity check that produced cone conforms to master cone

DMPlexOrientPointSF_Internal: fail if leave rank is me

DMPlexOrientPointSF_Internal: initialize leavesRanks to -2

DMPlexCheckPointSF called in DMPlexOrientPointSF_Internal if PETSC_USE_DEBUG

DMPlexOrientPointSF_Internal: remove PetscSF argument, instead obtained in the function body

DMPlexOrientPointSF_Internal: fix & improve the post-check

DMPlexOrientPointSF_Internal: correct orientation also in 3D

DMPlexOrientCell impl.

Adopted from my original approach haplav/fix-dmplex-distributed-interpolation

DMPlexOrientPointSF_Internal: only merge unneeded inner blocks

DMPlexOrientPointSF_Internal: always do post-check but only if PETSC_USE_DEBUG

DMPlexOrientPointSF_Internal: newcone -> cone

DMPlexOrientPointSF_Internal: compare leaves with roots, and their ranks, too