doc: migrate lib.attrsets to use doc-comments

[hsjobeki]

Description of changes

Doc-comment migration

cc @DanielSidhion

I am going to manually change the following after a the first round of review is done.

• Inner/outer format migrated /* {nixdoc} */ -> /** {commonmark} */
• Clean up function arguments. Manually remove the redundant line comments. We decided the codemod won't delete anything.
• Reify examples. After the migration is done all examples should be placed at the end under an # Examples heading.
  • Examples should be surrunded by :::{.example} such that they are properly styled.
  • Make sure examples have a descriptive heading. e.g. ## lib.asserts.assertMsg usage examples
• Manual reformatting work for consistency:
  • foldlAttrs: Attention block needs proper highlighting
  • Indentation: getAttrFromPath,
  • Whitespace: attrsToList
  • mapAttrsRecursive / mapAttrsRecursiveCond: inconsistent order of example / type. (Wont fix)

Please comment all other errors / mistakes.

NOTE: PRs should not add/change content (excluding minor fixes) so we keep track of eventual rendering problems arising with the migration in isolation.

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/)
• 24.05 Release Notes (or backporting 23.05 and 23.11 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.

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[hsjobeki]

@infinisil @DanielSidhion I think this PR should be ready to merge. If you'd give it a rough review.

I need to fix this in nixdoc: nix-community/nixdoc#113 but shouldn't be a blocker.

[DanielSidhion]

Looks good to me! No information lost and the formatting is great.

While reading through the changes I made a few suggestions of content to add (since the effort to write the suggestions was small and we're changing this stuff already).