This enhances the exisiting matc option "--debug" so that it includes
debug information in the resulting SPIR-V.
Previously we tied this to the build configuration which isn't very
flexible. Moreover this needs to be orthogonal to shader opts, because
we often need to debug problems that arise from optimization.
This CL also gives meaningful names to the ubershader materials and
fixes up the new matinfo analysis so that it prints the entire SPIRV
chunk that corresponds to each potentially problematic GLSL codeline.
Motivated by #1516.
b859b57797