ES3 supports set/get for both stencil and depth
attachments simultaneously though
GL_DEPTH_STENCIL_ATTACHMENT, so support for it
was added in FramebufferRenderbuffer and
GetFramebufferAttachmentParameteriv.

Change-Id: I09b077de1f31899a20baacbd651c65dfa9e7fc5d
Reviewed-on: https://swiftshader-review.googlesource.com/3546Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>