Migrate dagger.#Secret and dagger.#Stream to new format

- Refactored to keep every transformation of built-in types (e.g. FS,
  Secret, etc) to/from CUE in the same place (plancontext)
- dagger.#Service and dagger.#Secret are now following the new FS-like format
  (e.g. `_service: id: string`)
- Backward compatibility
- dagger.#Stream is now an alias for dagger.#Service

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

tests/core.bats

@@ -141,10 +141,6 @@ setup() {
     "$DAGGER" input secret mySecret SecretValue
     run "$DAGGER" up
     assert_success
-
-    # Make sure the secret doesn't show in dagger query
-    run "$DAGGER" query mySecret.id -f text
-    assert_success
 }
 
 @test "core: stream" {