LLVM: Move aliases to aliases.nix and switch to llvmPackages_latest

[primeos]

Motivation for this change

See #116736 (comment).

Unfortunately clang and llvm (s. "TODO" in the diff) are used to widely so moving those attributes requires someone who knows how to do mass renames (via rnix-parser, etc.).

E.g. this is still very inconsistent (mixing llvmPackages and llvmPackages_latest):

  clang = llvmPackages.clang;
  clang-manpages = llvmPackages.clang-manpages;
  clang-tools = callPackage ../development/tools/clang-tools {
    llvmPackages = llvmPackages_latest;
  };
  clang-analyzer = callPackage ../development/tools/analysis/clang-analyzer {
    llvmPackages = llvmPackages_latest;
    inherit (llvmPackages_latest) clang;
  };

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[SuperSandro2000]

This could also be done for discord.

[primeos]

Yes, I considered that but I'm not sure if it's worth it as discord/base.nix is called indirectly through discord/default.nix (and that way it's implemented might make this a bit tricky but it should be doable if necessary).

[primeos]

I'll drop this, not sure anymore if this is even a good idea (it would avoid some issues but likely also introduce new ones like making it harder to discover these aliases).