static Class getSiblingClass(Class c, S name, O classFinder default null) {
  ret getInnerClass(getOuterClass(c, classFinder), name, classFinder);
}

static Class getSiblingClass(O o, S name, O classFinder default null) {
  ret getSiblingClass(_getClass(o), name, classFinder);
}

Began life as a copy of #1004786