Move WGraphicBufferProducer from omx to bqhelper

In addition, make TWGraphicBufferProducer a template so that it can
inherit from any descendants of IGraphicBufferProducer so that it's
possible to avoid diamond inheritance while reusing the
implementation.

Test: adb shell am instrument -e size small -w 'android.media.cts/android.support.test.runner.AndroidJUnitRunner'
Change-Id: Iad5479735af1ae83f2175b1968a3e040d77a3bc0