The cube texture borders will be used for linear interpolation, in
order to produce seamless edges.

Change-Id: Idd17c72c6aaf7dcc65188b065ac8ba179b58cc37
Reviewed-on: https://swiftshader-review.googlesource.com/8209Tested-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>