Initial TextureSize parsing and implementation

Change-Id: I8b9b1808366b1013a5001e2dfa15a26d8471ab6a
Reviewed-on: https://swiftshader-review.googlesource.com/3753Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>