cue modules: move stdlib to pkg/alpha.dagger.io

In preparation for Europa, we will vendor multiple CUE modules:

- `pkg/alpha.dagger.io`: legacy non-europa packages
- `pkg/dagger.io`: core Europa packages
- `pkg/universe.dagger.io`: Europa universe

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

pkg/alpha.dagger.io/bats/tests/testfile/mods/bats-support/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "bats-support",
+  "version": "0.2.0",
+  "private": true
+}