rstudio: clean up and refactor

[TomaSajt]

The first 2 commits should not cause any rebuilds.
The 3rd commit should only cause rstudio-server to rebuild. (Since it now has empty arrays as desktopItems and qtWrapperArgs instead of them being undeclared)

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/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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.

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[b-rodrigues]

LGTM

[b-rodrigues]

pinging @ciil @drupol just to make sure this PR didn't fly under your radar

[TomaSajt]

I see that the rstudio server test is failing. I'm assuming it's not supposed to. Will check it out.

[TomaSajt]

Turns out rstudioWrapper expected the empty $out/share directory of rstudio-server (which I removed during the refactor) to exist. Now only the non-server version symlinks the share directory.
Fixed and rebased on latest master

[TomaSajt]

Rebased on master.

Is everything that worked before this PR still working?
I haven't checked since I can't really program in R and haven't used this program before.

If everything is OK, is there anything stopping us from merging?

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-already-reviewed/2617/2175

[jbedo]

Tested fully functional, previous issue of the visual editor being broken is resolved. LGTM.

[TomaSajt]

Okay, I'll try to merge it in a day if nobody objects to it.
(though, you can merge sooner if you want to, I just don't like self-merging quickly)

[Kupac]

Visual editor is finally working. I used to have problems with the built-in debugger (it didn't show up in the environment browser), which is also fixed in this PR. LGTM!

PS: compilation needs more RAM than previously. Restricting the number of cores helps.

[TomaSajt]

Next step will be #362637, though we need to wait for electron to get cached.