RFC: add a vulkan layer to trace all Vulkan commands
This layer traces all known Vulkan commands using Perfetto. I plan to use it to study frame times.
This is RFC because it is just a Vulkan layer and does not necessarily belong to Mesa. But if people find it useful, why not? If there are interests, I will clean it up a bit and drop the RFC tag. I will also probably make vkCmd* tracing optional as they are more noisy and more performance critical.