[C++] Allow disabling extension type deserialization when reading IPC

### Describe the enhancement requested

Certain users of the IPC format may want to entirely prohibit deserialization of extension types, or adopt a selective whitelist approach when loading extension types.

This may come up useful when there is a concern that some third-party extension types may have latent robusteness issues in their deserialization code.

### Component(s)

C++