Need to make more interfaces to work with the canvas

[artrointel]

https://github.com/artrointel/CanvasOverGLES/blob/a6a07dab393f4c17009de382da07cb1e9d790070/app/src/main/java/com/artrointel/canvasovergles/glview/renderers/CanvasRenderer.java#L64

public void setCanvasBufferUpdatedListener(@nullable CanvasBufferUpdatedListener listener) {
mSurfaceTextureListener = listener;
mSurfaceTexture.setOnFrameAvailableListener(mSurfaceTextureListener); // call updateTexImage() to render canvas by ext. image safely. should be called in gl thread.
}

and also have

public void unlockCanvasAndPost() {
unlockCanvasAndPostInternal();
if(mSurfaceTextureListener == null) {
// unsafely update if there is no listener.
mSurfaceTexture.updateTexImage();
}
}

[artrointel]

done