Fragment and Vertex inputs and outputs were treated as OpenGL ES2.0
attributes and varyings, but OpenGL ES3.0 inputs and outputs have
different limitations and must be treated differently. This cl simply
introduces the new types, without modifying the ES2.0 behavior and
only modifying ES3.0 to allow integer varyings when they are flat.

Change-Id: I965cb576bab3f505602af9e055438bcc7c18cdfd
Reviewed-on: https://swiftshader-review.googlesource.com/3371Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>