pkgs/top-level/stage.nix: rename mkMuslParsedPlatform, improve comment

[amjoseph-nixpkgs]

Description of changes

The existing name and descriptive comment for mkMuslParsedPlatform are not so great, and has led to people misunderstanding what it does.

Let's help ensure that additional case-branches are added correctly in the future by explaining what this function is supposed to do.

Things done

• Built on platform(s)
  • [ ] x86_64-linux
  • [ ] aarch64-linux
  • [ ] x86_64-darwin
  • [ ] aarch64-darwin
• [ ] For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• [ ] 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/)
• 22.11 Release Notes (or backporting 22.05 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
  • [ ] (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• [ ] Fits CONTRIBUTING.md.

[ghost]

Resolved merge conflict.

[ghost]

Resolved merge conflict.