Collect depth and stencil values before/after.

* This code is just to test if the method works, it's super ugly and needs
  to be tidied up (as does this whole function!)
Pass stencil as int32_t so depth or stencil of -1 indicates no data
Add RGBA value prefixes, only print valid elements, preview depth
register(bX) for cbuffers, only bind and copy stencil when valid