internal/core/export: explicit generation of adt types

Change-Id: Ib51a41d9103c6f9e684395a009c8c3b81462c273
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6622
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
diff --git a/internal/core/export/testdata/scalardef.txtar b/internal/core/export/testdata/scalardef.txtar
index 3e5b5b3..b328ff5 100644
--- a/internal/core/export/testdata/scalardef.txtar
+++ b/internal/core/export/testdata/scalardef.txtar
@@ -22,6 +22,8 @@
 []
 [#pkg1]
 -- out/definition --
+package test
+
 import pkg2 "example.com/foo/pkg1"
 
 "Hello \(#pkg1)!"