add vscode extension and vim plugin packages to nix flake outputs

[fidgetingbits]

Now that cursorless.nvim is merged, the flake.nix can be updated to expose the vim plugin so it can be used directly from declarative nix config. It's more suited to be done this way than put it in nixpkgs because of rolling release.

At the same time should add the vscode extension building and expose it as a separate package