New widget: TextureView

Bug #4343984

TextureView can be used to render media content (video, OpenGL,
RenderScript) inside a View.

The key difference with SurfaceView is that TextureView does
not create a new Surface. This gives the ability to seamlessly
transform, animate, fade, etc. a TextureView, which was hard
if not impossible to do with a SurfaceView.
A TextureView also interacts perfectly with ScrollView,
ListView, etc. It allows application to embed media content
in a much more flexible way than before.

For instance, to render the camera preview at 50% opacity,
all you need to do is the following:

mTextureView.setAlpha(0.5f);
Camera c = Camera.open();
c.setPreviewTexture(mTextureView.getSurfaceTexture());
c.startPreview();

TextureView uses a SurfaceTexture to get the job done. More
APIs are required to make it easy to create OpenGL contexts
for a TextureView. It can currently be done with a bit of
JNI code.

Change-Id: Iaa7953097ab5beb8437bcbbfa03b2df5b7f80cd7