bats: Add library wrapper

Adds a `bats.withLibraries (p: [ ... ])` function, which creates a
`bats` wrapper where the `BATS_LIB_PATH` environment variable contains
fallbacks for the given list of libraries.

This allows to e.g. use the `bats-assert` library (which itself requires the
`bats-support` library) with

    bats.withLibraries (p: [ p.bats-support p.bats-assert ])

In a `.bats` file you can then call `bats_load_library` [1] to load the
libraries in the `setup()` function:

    setup() {
      bats_load_library bats-support
      bats_load_library bats-assert
    }

[1]: https://bats-core.readthedocs.io/en/stable/writing-tests.html?highlight=library#bats-load-library-load-system-wide-libraries

pkgs/development/interpreters/bats/default.nix

@@ -14,6 +14,8 @@
 , bats
 , lsof
 , callPackages
+, symlinkJoin
+, makeWrapper
 , doInstallCheck ? true
 }:
 
@@ -108,6 +110,24 @@ resholve.mkDerivation rec {
 
   passthru.libraries = callPackages ./libraries.nix {};
 
+  passthru.withLibraries = selector:
+    symlinkJoin {
+      name = "bats-with-libraries-${bats.version}";
+
+      paths = [
+        bats
+      ] ++ selector bats.libraries;
+
+      nativeBuildInputs = [
+        makeWrapper
+      ];
+
+      postBuild = ''
+        wrapProgram "$out/bin/bats" \
+          --suffix BATS_LIB_PATH : "$out/share/bats"
+      '';
+    };
+
   passthru.tests.upstream = bats.unresholved.overrideAttrs (old: {
     name = "${bats.name}-tests";
     dontInstall = true; # just need the build directory