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/.travis.yml

@@ -0,0 +1,7 @@
+language: bash
+before_install:
+  - ./script/install-bats.sh
+before_script:
+  - export PATH="${HOME}/.local/bin:${PATH}"
+script:
+  - bats test