Fix point merge for Marching Cubes with multiple isosurfaces

When the Marching Cubes algorithm merges points together for multiple
isosurfaces, it uses an ArrayHandleZip to combine the isosurface id and
the edge identification. This is to prevent merging points from
different isosurfaces. However, internally this has to do an array copy.

It was doing this copy with `ArrayCopy`. A recent change to that method
made the copy fail for `ArrayHandleZip`. The fix is to change to
`ArrayCopyDevice`.

The reason why this bug was introduced was because there was no test
case for this specific use. A regression test has been updated to test
for this case.
9 jobs for fix-mc-merge