Motivation for this change

Upstream did a lot of great cleanup on the main vulkan packages, factoring them out properly and supporting separate compilation gracefully. shaderc didn't, but I unbroke and updated it anyway to celebrate. I wasn't able to get the tests running--some sort of linker path weirdness--but things seem to otherwise be working.

One slightly weird thing I'm doing here is copying the headers (but no other data) from vulkan-headers into the dev output of vulkan-loader. This maintains backwards compatibility and seems to be consistent with the expectations of the upstream packages, but isn't ideally normalized.

vulkaninfo is now provided by vulkan-tools instead of vulkan-loader.

I don't expect any downstream breakage, but it would probably be prudent to test at least a few dependent packages.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.