Instead of passing SamplerInterfaceBlocks and a SamplerBindingMap to
Program, we now set a 'sampler group' per binding point:
Program::addSamplerGroup(...)
A sampler group here consists of a list of N 'Sampler' and a 'Sampler'
is just a unique name (unifrom name in the shader) and binding point in
the shader.
That's all the driver layer needs.
With this change we get rid of the code that re-created the uniform
names in the driver -- this should never have been done there. And we
also remove the hash-map lookups in vulkan and metal drivers.
2a72e8aee8