texlive: some small refactors

[apfelkuchen6]

Description of changes

These changes move some code around to make texlive more managable. This should not cause any rebuilds.

This is split off from the texlive scopification PR I'll create right after this in the hope that this can be merged almost immediately and I won't have to rebase these commits.

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/)
• 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.

[apfelkuchen6]

One of the test fails on my machine, but also did before this PR:

texlive-test-binaries> building '/nix/store/6a16fffzdsh183b7jjb86hsp80nkg96b-texlive-test-binaries.drv'
texlive-test-binaries> failed 'pdfclose --version' (exit code: 1)
texlive-test-binaries> tested 436 binaries: 17 ignored, 2 broken, 1 failed

[xworld21]

Very useful and overdue, and with zero user visible changes so safe to merge quickly.

@GrahamcOfBorg build tests.texlive.licenses

[veprbl]

LGTM

[veprbl]

Please rebase