fuse: use macfuse-stubs instead on Darwin

[midchildan]

Motivation for this change

Replaces the Linux-only fuse package with macfuse-stubs on Darwin. This should further increase the number of FUSE packages available on Darwin, although more fixes would probably be needed on a per-package basis.

macfuse-stubs should mostly work as a drop-in replacement for fuse. However, it isn't yet compatible with libfuse 3.x, so packages that depends on fuse3 would still be unsupported on Darwin.

It should be noted that macFUSE would need to be installed outside of Nix in order to run FUSE packages. macFUSE isn't packaged in Nix because it includes a kernel extension, which isn't supported by Nix outside of NixOS. I don't know how best to warn users of this, but I added brief explanation in the longDescription of macfuse-stubs.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[SuperSandro2000]

I don't know how best to warn users of this, but I added brief explanation in the longDescription of macfuse-stubs.

Things done

This isn't enough for depending packages but I don't have a better idea right now.

[midchildan]

I pushed a new commit including a new section in the manual for FUSE with an advice about macFUSE. Maybe this can help.