GlobalFiles is a global registry of file descriptors.

GlobalTypes is the registry used by default for type lookups unless a local registry is provided by the user.

NotFound is a sentinel error value to indicate that the type was not found.

Files is a registry for looking up or iterating over files and the descriptors contained within them.

Types is a registry for looking up or iterating over descriptor types.

ExtensionTypeResolver is an interface for looking up extensions.

MessageTypeResolver is an interface for looking up messages.