layers: Require pipeline layout to contain all referenced descriptors

layers: Require pipeline layout to contain all referenced descriptors

If the SPIRV image uses a descriptor (for constant buffer, image, etc)
we must declare it in the pipeline layout.

We won't complain about unused junk in the pipeline layout, but not
declaring something that *is* used is an error.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Courtney Goeltzenleuchter <courtney@lunarg.com>