Draft: Rework MediaCodec download code

see #26934

This is not the final version of the code.

I know there's a lot wrong with it, but for now, my goal is simply to render a frame, even if it's incorrect.

I'm trying to use the AImageReader API, but I'm stuck. For some reason, the AImageReader callback never executes. I also tried polling without any conditional variable using acquireLatestImage in OutThread. In that case, it always returns AMEDIA_IMGREADER_NO_BUFFER_AVAILABLE.

I’m not sure what I’m doing wrong. Could you guys provide some guidance?