Added Shaderc to tests in order to enable online shader builds

[axsaucedo]

Edit: Decision was to go with #154

Fixes #150
Fixes #121

Aims to add shaderc in tests as dependency to enable all current tests to work in the CI.

This was also an attempt to explore whether shaderc could be adopted as a dependency, but it seems that shaderc has too many dependencies, including glslang, glslc, spirv-tools and many others. This increases the binary of the tests from 3mb to 11mb which is quite significant.

The existing PR #112 adds support only to GLSLang compiler from Khronos group, and seems to only add 2-3 mb, and only requires a single dependency making it more appealing. @alexander-g suggests that pyshaderc is faster to compile, but it seems that shaderc is based on glslc and hence glslang so it may be worth exploring further as it may be more feasible to just add glslang instead.

Outstanding:

• Explore replacing shaderc with glslang after confirming tradeoffs on features and compilation speed
• Remove all references to char and replace by uint32_t for inputs to data
• Explore adding glslang as core dependency inside kompute to ensure it's well maintained

[axsaucedo]

After further assessment the decision is to go ahead with glslang #154 - the main reason is as this significantly reduces compilation times massively, as well as the maintenance burden, whilst providing the same base functionality as core. This means that the initial implementation won't have thread-safe support, however it will still support the #include supoprt, and this feature can be introduced later on potentially as more people adopt this functionality.