[NRBF] Reject orphaned records and invalid references

[adamsitnik]

A brief explanation of how I've implemented it:

• The first record we read, must be an NRBF header. It provides RootId, but nothing else (its type etc).
• From here, the payload can contain BinaryLibraryRecord at any point.
• If the first actual record is a ClassRecord with any members or ArrayRecord with any items, a stack is being populated with information of expected record type. We read those records and if there is a type mismatch, we throw.
• Most records may contain references, in such a case we store information about what is the expected record type (what the reference should be pointing to) and store the reference in record map.
• We read the referenced records and if there is a type mismatch (example: an array of strings containing a reference to binary library), we throw.

@GrabYourPitchforks PTAL and let me know if you have any concerns. I would be happy to convert specific scenarios into test cases.

[adamsitnik]

this check is no longer needed here, as there is a universal check for all references in RecordMap.Add. The benefit is that we throw as soon as we encounter an invalid reference.

[jeffhandley]

We are going to discuss this further to decide if we want to change this logic in .NET 9 or document that the decoder does not reject these records. We could potentially add this logic in .NET 10 with the PayloadOptions offering a setting for whether or not they should be rejected.

This is therefore not blocking the release.