Basic shell classes for Pipeline, PipelineLayout

b/118386749

Change-Id: I1ec82d1bf2334d5e2cd338d96eff63f3714db198
Reviewed-on: https://swiftshader-review.googlesource.com/c/21888Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>