Add correct inspect methods for BSON Types

The previous Object.defineProperty() calls did not work because
they did not specify a property descriptor, and even if they had
worked, the signatures of .inspect() and .toString() would
have mismatched, and even if they weren’t, the result would not
have been very useful as debugging output, because it only returned
the raw hex content of the ObjectId and not even e.g. the fact
that this object is an ObjectId.