title: in-place processing of a Metal texture
body: <p>Is it possible to process an <code>MTLTexture</code> in-place without <code>osx_ReadWriteTextureTier2</code>?</p>
  
  <p>It seems like I can set two texture arguments to be the same texture. Is this supported behavior?</p>
  
  <p>Specifically, I don't mind not having texture caching update after a write. I just want to in-place (and sparsely) modify a 3d texture. It's memory prohibitive to have two textures. And it's computationally expensive to copy the entire texture, especially when I might only be updating a small portion of it.</p>