internal/core/adt: add tests for issue 3834

Issue #3834

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I9bdaa8c4f901db4417e044ab5ca45bc2a97336f1
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1211932
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: mpvl