WIP: Use piglit shader_runner tests in CI

[alixinne]

PR to discuss the implementation of a solution for #34

The parser from piglit seems to be more strict than just basic syntax checking, so a lot of the tests currently fail because we're lacking semantic analysis.

Some errors are also due to the current representation of the preprocessor directives and are thus "expected".

[hadronized]

Semantic analysis is something I want in the crate eventually. The idea is that SPIR-V will require it, so we need to have some ways to do it and I think it’s a whole complex problem. I haven’t really started to work on it, even though I have been having it on my mind for a while.

Thanks for the PR!