mrtrix: init at 3.0_RC3_latest

[bcdarwin]

Motivation for this change

Add a package. (Note that the slightly strange-looking version is in fact a valid Git tag.)

This package consists mostly of command-line tools, but there are also two qt5-based image viewers (mrview and shview). I have provided an option withGui ? true to allow users to disable these viewers (primarily in order to remove Qt from the closure). They work on NixOS but are unlikely to work out-of-the box on non-NixOS Linux (see #62169), but I've refrained from asserting that they shouldn't be built since a user might want to fiddle with runtime GL stuff.

Some programs rely on FSL and/or ANTs backends; I have somewhat heavy-handedly wrapped all binaries to point to ANTs, while FSL is not available in Nix at the moment and has a non-commercial license so would be convenient to disable by default for Hydra builds.

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
• [NA] Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• [NA] 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/)
• [NA] Determined the impact on package closure size (by running nix path-info -S before and after)
• [NA] Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[lheckemann]

Given the odd name of the version, can we be sure that the tag won't be replaced in the future?

[bcdarwin]

@lheckemann - fair point, but it hasn't been updated in a while and an RC4 is out (but they've labelled it broken/internal use only). I could change to use the commit instead?

[lheckemann]

That does sound unlikely to change, so I'm fine with using this.