Related issue #108606.
Nowadays we have multiple outdated versions of Flutter in nixpkgs.
Instead, let's focus in having in having stable versions of Flutter
working.
Users needing to use beta or dev versions of Flutter can use mkFlutter
function, that still exists.
flutter: add beta and dev channels
flutter: artifacts are now downloaded in $HOME/.cache/flutter
flutter: remove all artifacts from flutter
flutter: fix lockfile path
flutter: fix pub_cache
flutter: fix flutter_tools/.packages pointing to /build
flutter: clean patches
flutter: fix write error on .cache/flutter/lockfile
flutter: add zlib as a dependency
flutter: add missing dependencies
flutter: fix flutter version
flutter: update versions + dependencies