Currently, resetting the internal state related to the codec in done in 4 places
in MediaCodecRenderer:
1. In the constructor to set some sensible initial default.
2. In flushOrReleaseCodec to reset state after flushing
3. In releaseCodec to reset state to default values for a released codec.
4. In initCodec to reset state to defaul values for a new codec.
There are actuall only two types of state reset operations:
1. Resetting state for a released codec, so that a new codec isn't influenced by
previous codecs.
2. Resetting state after flushing an existing codec. This is a subset of (1).
So to simplify the class, this change moves all state resets to two methods
corresponding to the two cases above.
PiperOrigin-RevId: 285731913
