[stdlib] Kill O(N) bridging [SomeClass] to ObjC

There's no need for a deferred conversion in these cases.

stdlib/public/core/ContiguousArrayBuffer.swift

@@ -433,8 +433,10 @@ struct _ContiguousArrayBuffer<Element> : _ArrayBufferProtocol {
         _isBridgedToObjectiveC(Element.self),
         "Array element type is not bridged to Objective-C")
     if count == 0 {
-      return _SwiftDeferredNSArray(
-        _nativeStorage: _emptyArrayStorage)
+      return _emptyArrayStorage
+    }
+    if _isBridgedVerbatimToObjectiveC(Element.self) {
+      return _storage
     }
     return _SwiftDeferredNSArray(_nativeStorage: _storage)
   }