Added basic class / enums / function skeletons
for Texture2DArray. No sampling code has been
added to SamplerCore for Texture2DArray yet.

Change-Id: I78bc1fdec069005d2b3b6f6b1ba41db8c278f74b
Reviewed-on: https://swiftshader-review.googlesource.com/2852Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>