cue/testdata: add regression test for issue 2209

The full reproducer worked on CUE v0.4.3 and broke in v0.5.0.
It is still broken as of today with evalv2, but it works on evalv3.

Add the reduced version as well, as it is easier to comprehend.

Closes #2209.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I875510a75b228cf54a6b3ef4a56d97d4ae03b8ad
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1214407
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan