SDK / exoplayer

The restriction that these classes only work with SimpleDecoders
is unnecessary. An FfmpegVideoRenderer will not be able to use a
SimpleDecoder, because the SimpleDecoder assumption that each input
buffer can be decoded immediately into a corresponding output is
not true for all video codecs that Ffmpeg supports (e.g., H264 does
not have this property). Generalizing SimpleDecoderVideoRenderer to
DecoderVideoRenderer will allow FfmpegVideoRenderer to still use
the base class, without having to use a SimpleDecoder.

This is a preliminary change toward being able to merge a version
of https://github.com/google/ExoPlayer/pull/7079.

Issue: #2159
PiperOrigin-RevId: 301412344