Pointers to hide status layers and custom data are removed,
since they can be accessed from the mesh as necessary.
Usage of other arrays has been reduced, so the pointers
can eventually be removed.
The reasoning is the same as some other commits in this area:
the goal is less duplication of state, and a more focused design
of the responsibilities of the PBVH class.
Some of the changes are fairly noisy, since we need to add
arguments to functions in a few places. On the nicer side of
things, some functions for syncing the state can be removed.
Not retrieving hide layers with write access also has performance
implications in some cases, since it means the original arrays can
be reused without a copy when they're shared.
49f676e6c2