This adds the ability to render to a specific layer of a 2D array
texture.

Change-Id: I3055d62c9964b2729704785efb068b82eef4f9ce
Reviewed-on: https://swiftshader-review.googlesource.com/14668Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>