Instead of having to manually stub packages that should not be
downloaded we instead automatically stub all packages (except a small
list of whitelisted ones). Tests can re-introduce the real package by
using the `realPkgs` module argument.
Add an option to programs.autorandr's configModule to allow arbitrary
extra config lines.
No option exists for adding arbitrary key/values to generated autorandr
profile config, as is common in other nix modules. This commit adds one.
This option provides a more convenient way to overlay dummy packages.
It also adds a function `config.lib.test.mkStubPackage` that can,
e.g., be used for `package` options.
