apple-sdk: Include man pages starting from version 15

[zhaofengli]

Apple SDKs include man pages for command-line utilities shipped with macOS as well as APIs, many of which are not available in source releases. It would be nice to have them in apple-sdk.

Since those man pages may conflict with those provided by Nixpkgs, we split them into a separate output named sdkman to avoid polluting devShells by default. In order to minimize rebuilds, the change is also gated to SDKs starting from version 15.

The man pages themselves appear to be compressible:

$ nix-store --dump /nix/store/26940l0019wnn7sg41x7zcz5ywimaxl3-apple-sdk-15.2-sdkman > apple-sdk-15.2-sdkman.nar
$ zstd apple-sdk-15.2-sdkman.nar -o apple-sdk-15.2-sdkman.nar.zst
apple-sdk-15.2-sdkman.nar : 58.24%   (  46.6 MiB =>   27.1 MiB, apple-sdk-15.2-sdkman.nar.zst)

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/)
• Nixpkgs 25.11 Release Notes (or backporting 24.11 and 25.05 Nixpkgs Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
• NixOS 25.11 Release Notes (or backporting 24.11 and 25.05 NixOS Release notes)
  • (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.

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[zhaofengli]

With #409574 merged, I reworked the PR to return to determining whether the fetched SDK has man pages with src.passthru.includeMan. This feels cleaner to me - fetch-sdk is responsible for pruning the raw SDK and can potentially be overridden, and it should therefore be the source of truth of whether the man pages are actually included.