tvOS does not support tessellated drawing from indirect buffers

Specifically...the `drawPatches:...indirectBuffer:...` style methods are not available.

@cdavis5e I'll defer to your implementation expertise on this one.

Do we need a portability flag for this? Or is a workaround possible?

@kvark commented:
> Does tvOS even have GPU-local memory? If it doesn't we can just read the contents of the `indirectBuffer` on CPU and behave accordingly.

Start by examining the tvOS limitation around the drawPatches:...indirectBuffer: methods and how indirectBuffer contents are handled. Determine whether a portability flag or a CPU-side workaround is appropriate, then document the resulting behavior and verify it against the tvOS support constraint described here.

Written by the indexing model from the issue text.