camera2-portability: Add support for previews using the camera2 API

At the moment, only SurfaceTextures (and not SurfaceViews/SurfaceHolders) are
supported. The tests still only cover Stringifier and IntegralStringifier.

Change-Id: Ie643c58f8383cd3b9f59c16e0b79239df0ca068d
18 files changed