Breaking change docs: CborReader/CborWriter enforce default maximum nesting depth (.NET 11)

[Copilot]

Documents the .NET 11 Preview 5 breaking change where CborReader and CborWriter now enforce maximum nesting depths by default (64 and 1000, respectively), throwing CborContentException and InvalidOperationException when exceeded.

Changes

• New article docs/core/compatibility/extensions/11/cbor-max-depth.md — covers previous/new behavior, affected APIs, and how to configure a higher limit via the new CborReaderOptions/CborWriterOptions types
• docs/core/compatibility/11.md — adds entry under Extensions
• docs/core/compatibility/toc.yml — adds entry under .NET 11 Extensions

Key callout documented

Unlike Utf8JsonReader/Utf8JsonWriter, MaxDepth = 0 means no nesting allowed (not "use the runtime default"). Users who need deeper nesting must opt in explicitly:

var options = new CborReaderOptions { MaxDepth = 256 };
var reader = new CborReader(data, options);

var writerOptions = new CborWriterOptions { MaxDepth = 2000 };
var writer = new CborWriter(writerOptions);

There is no AppContext switch to restore unlimited-depth behavior.