Basic shell class for ShaderModule

Bug b/118386749

Change-Id: Ia41957ba1ef3be179d20c37cea0227a9a4509c7b
Reviewed-on: https://swiftshader-review.googlesource.com/c/22609Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>