dart: add update script

[gilice]

Description of changes

Adds an updater-script for dart. Update-source-version won't cut it because it cannot handle multi-source.

Things done

• Built on platform(s)

  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin

• 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/)

• 23.05 Release Notes (or backporting 22.11 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.

[gilice]

Extra-good because r-ryantm should pick it up right after the merge, since t here's 2.19.4 now

[wegank]

I'm afraid this won't work, the update script should also update the hashes (via update-source-version)...

[gilice]

Oh that is very true. Kinda forgot that ...... Doing now.

[gilice]

@wegank I tried a different approach.
Ready for re-review