rust-analyzer-unwrapped: optional proc-macro-srv-cli

[arcnmx]

Description of changes

Resolves a crash related to rust-lang/rust-analyzer#14991

:; export RUST_ANALYZER_INTERNALS_DO_NOT_USE='this is unstable'
:; nix shell .#rust-analyzer-unwrapped -c rust-analyzer-proc-macro-srv < /dev/null

thread 'main' panicked at 'proc-macro-srv-cli requires the `sysroot-abi` feature to be enabled', crates/proc-macro-srv-cli/src/main.rs:23:5

Unfortunately, the server isn't able to compile without unstable rust so I've chosen to disable it by default since it's currently broken - though I don't personally have a preference on whether to enable or disable it by default? Another approach is to pull the macro server out into an entirely seperate package, though that may be inefficient since both binaries share common dependencies.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.