scope getDeclaredConstructors_cached

// TODO: convert to regularly cleared normal map
static Map<Class, Constructor[]> #cache = newDangerousWeakHashMap();

static Constructor[] getDeclaredConstructors_cached(Class c) {
  Constructor[] ctors;
  synchronized(cache) {
    ctors = cache.get(c);
    if (ctors == null) {
      cache.put(c, ctors = c.getDeclaredConstructors());
      for (ctor : ctors)
        makeAccessible(ctor);
    }
  }
  ret ctors;
}

Began life as a copy of #1005587