New class ScopedJavaRefCounted

Intended to be used for holding on to references to the java
EncodedImage and call its release method when no longer used by C++.

Bug: webrtc:9378
Change-Id: I40d917c2bb4217419ef2d609e517566c8466a274
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/154740
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29347}

sdk/android/api/org/webrtc/RefCounted.java

@@ -24,5 +24,5 @@ public interface RefCounted {
    * Decreases ref count by one. When the ref count reaches zero, resources related to the object
    * will be freed.
    */
-  void release();
+  @CalledByNative void release();
 }