Fix start/pause behavior for AnimatedImageDrawable

Bug: 63908092
Test: HwAccelerationTests

Do not start the animation at creation time

When starting, first update the time, so it doesn't think we skipped a
bunch of frames if we're resuming.

Continue storing the SkPicture when stopped, so that we can continue to
show the same frame, without a jump.

Change-Id: I5ac77f2561fc9f42f8f69ebfbee21fe647cfc75a