isAbstract property
Whether the bridged native class is abstract (cannot be instantiated
directly).
Plan I: when an interpreted subclass calls super() against an abstract
bridged base whose generator emitted no constructor adapter (because of
GEN-051's abstract/sealed skip rule), the runtime treats the super-call
as a no-op — the abstract type can never be constructed natively, so
the subclass's own proxy/state is what carries the bridged identity.
Mirrors the existing D4.hasInterfaceProxy fallback behaviour for the
case where no proxy is registered.
Implementation
final bool isAbstract;