internal/core/adt: add tests for matchN

Add tests that should show both incomplete and
final errors.

This also tests that disjunctions are allowed as
bounds (they are not).

Issue #3409

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I99e3d85171b1436c0c0f77adb9c4f4b88dc68d9f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1200348
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>