shaderc::SpvModule should be renamed to shaderc::CompilationResult

[dneto0]

The class is the result produced from compilation: status information plus the actual bits generated by the compiler. Those bits are usually a SPIR-V module. However, it can be something else, e.g. when doing the equivalent of -E (preprocess-only) or -M (target dependencies).

This change would go along with the (in-flight) rename of shaderc_spv_module to shaderc_compilation_result
#126

[dekimir]

https://github.com/google/shaderc/pull/126/files#diff-13a2c8c8e3e8b2cf2d0483a74140ee9eL26