And call it overrideArgs in the let binding because that's what it does

This allows querying the arguments you can .override:

  nix-repl> lib.functionArgs pkgs.hello.override
  { fetchurl = false; stdenv = false; }

…ction

This allows querying function arguments of things like fetchFromGitHub:

  nix-repl> lib.functionArgs pkgs.fetchFromGitHub
  { fetchSubmodules = true; githubBase = true; ... }

…tions

- Apparently nobody ever needed this
- We already have enough ways to override things
- Using overrideDerivation is discouraged

- Rename ff to result because that's what it is
- Better indentation
- Less parens
- Comment what overrideWith does

lib.makeOverridable: Propagate function arguments