Optionally add default case to all case analyses

In #20598 (closed) we noticed a bug which resulted in worker-wrapper incorrectly producing a case analysis which failed to cover all alternatives that might occur at runtime. Consequently, we ended up generating code which misbehaved at runtime, leading to a non-trivial debugging process.

This would all have been much easier to debug if we had a code generation option to introduce default cases to all case analyses which lack them.