Cluster Objects don't handle unknown enum/bitmap values well

[mrjerryjohns]

Problem

When decoding cluster elements that are of type enum* or bitmap* using the generated stuff in cluster-enums.h or cluster-objects.h, enum values that are not recognized still get silently decoded without any conveyance of failure.

This can result in un-defined behavior in application logic that is unaware that the decoded value is not actually valid against their compiled-in definition of that enumeration/bitmap.

While this won't practically be a problem till post 1.0, it's important to solve it before 1.0 since clients need to be built to be defensive now since upgrading them later is likely not always possible.

[woody-apple]

Spec Issue Review: Per @bzbarsky-apple we should confirm that this is a spec compliance issue, if not, remove the label. Still makes sense for 1.0 for forwards compatibility.

[mrjerryjohns]

With #20907 merged, this issue is complete.

[bzbarsky-apple]

@mrjerryjohns I don't think the bitmap part of this is done....