Merge "Camera: Clarify benefit of readout vs exposure timestamp" into tm-d1-dev

         * {@link #onCaptureStarted}. Unlike {@link #onCaptureStarted}, instead of passing

         * a timestamp of start of exposure, this callback passes a timestamp of start of

         * camera data readout. This is useful because for a camera running at fixed frame

         * rate, the start of readout is at fixed interval, but not necessary for the start

         * of exposure.</p>

         * rate, the start of readout is at fixed interval, which is not necessarily true for

         * the start of exposure, particularly when autoexposure is changing exposure duration

         * between frames.</p>

         *

         * <p>This timestamp may not match {@link CaptureResult#SENSOR_TIMESTAMP the result

         * timestamp field}. It will, however, match the timestamp of buffers sent to the