cmd/cue: add edge case tests for embed attributes
These exhibit behavior that changes with the next CL in this chain.
Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I226190ef6c477d2f2b0051c8be424ab2748ff335
Reviewed-on: https://cue.gerrithub.io/c/cue-lang/cue/+/1233922
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
Reviewed-by: Matthew Sackman <matthew@cue.works>