This updates the test to use the new public GetGlslIoMapper() and
TProgram::getGlslIoResolver() entry points, instead of depending on
internal points that are not available in shared library builds.
Remove the dependency on LiveTraverser.h, which transitively includes
localintermediate.h. As a result, some things have been moved from
iomapper.h to iomapper.cpp, specifically the TVarEntry type and the
constructor and destructor of TGlslIoMapper.
If an 'in' is present in a shader stage, make sure a matching 'out'
is present in the previous stage. Only enabled when doing Vulkan.
This commit also fixes a bug where previous stage's linkerObjects
got polluted with 'in' variables from the next stage when merging
linker objects.
