create mkVSCodeFork and code-cursor

[emaiax]

Description

Based on #6355, all logic from vscode/default.nix was extracted to vscode/mkVSCodeFork.nix that can be reused to quickly build more VS Code compatible forks.

Given the number of VSCode flavors (Codium, Cursor, Windsurf, etc.), this makes it very easy for anyone to store and manage their editor configurations.

This PR also introduces code-cursor.nix config.

ref: #5684

Checklist

• Change is backwards compatible.
• Code formatted with nix fmt or nix-shell -p treefmt nixfmt deadnix keep-sorted --run treefmt.
• Code tested through nix-shell --pure tests -A run.all or nix build --reference-lock-file flake.lock ./tests#test-all using Flakes.
• Test cases updated/added. See example.
• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module
  • Added myself as module maintainer. See example.