*** Original commit ***
Rollback of https://github.com/google/ExoPlayer/commit/3bb0210d229ffd1455d546fa738dfebbac50f552
*** Original commit ***
Move SimpleExoPlayer logic into ExoPlayerImpl
This makes SimpleExoPlayer a simple forwarding wrapper which can be
removed in the future.
The changes are all purely mechanical with none of the potential further
simplifications made yet...
***
PiperOrigin-RevId: 427131338
