Updated screenshot code to reflect native changes.

The changes in native code removed using a GraphicBufferProducer and
instead use only a GraphicBuffer to generate screenshots. Updated JNI
code so it calls the screensot function that returns a GraphicBuffer
and handle returning either a Surface, GraphicBuffer, or Bitmap.

Also updated screencap shell code so it uses the new GraphicBuffer
screenshot code.

Test: Recents, screenshot from SystemUi, screenshot from shell.
Change-Id: I6cb4f619e59461790a2a8f0cd2ea1192d9ae66b6