aco: add framework for unit testing

Instead of compiling and running shaders, tests made with this framework look at the shader IR or assembly instead. This is useful for simultaneously testing that optimizations are correct and that they actually happen. They can also be run without an AMD GPU, so it should be possible to run them in the Gitlab CI or run tests targeting a specific family without ever needing a different GPU to be installed

Although RADV is built in meson-arm64, the tests are disabled in meson-arm64 because glslang isn't available

The tests are disabled by default and are enabled independently from the other tests using the build-aco-tests option